{"gene":"IL33","run_date":"2026-04-28T18:06:54","timeline":{"discoveries":[{"year":2005,"finding":"IL-33 was identified as the functional ligand for the orphan IL-1 receptor ST2; binding activates NF-κB and MAP kinases and drives production of TH2-associated cytokines (IL-4, IL-5, IL-13) in vitro and in vivo.","method":"Receptor-ligand binding assays, NF-κB reporter assays, in vivo cytokine measurement in mice","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 1-2 — foundational discovery with multiple orthogonal assays, highly replicated (3006 citations)","pmids":["16286016"],"is_preprint":false},{"year":2006,"finding":"IL-33 is a chromatin-associated nuclear factor (identical to NF-HEV) with transcriptional repressor properties; nuclear localization and heterochromatin association are mediated by an evolutionarily conserved homeodomain-like helix-turn-helix (HTH) motif in the N-terminal domain.","method":"Immunostaining with multiple antisera, live-cell imaging, co-localization with mitotic chromatin, transcriptional repressor assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods (immunostaining, live imaging, functional repressor assay), replicated extensively","pmids":["17185418"],"is_preprint":false},{"year":2007,"finding":"IL-1 receptor accessory protein (IL-1RAcP) forms a co-receptor complex with ST2 to mediate IL-33 signal transduction; IL-1RAcP is required for IL-33-induced in vivo effects and dominant-negative IL-1RAcP blocks IL-33 signaling.","method":"Co-immunoprecipitation, dominant-negative constructs, in vivo functional assays","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP plus dominant-negative rescue, widely replicated","pmids":["17675517"],"is_preprint":false},{"year":2007,"finding":"Soluble ST2 (sST2) directly binds IL-33 in the fluid phase, preventing it from interacting with membrane-bound ST2L and thereby suppressing NF-κB activation and Th2 cytokine production.","method":"Direct binding assay (soluble ST2–IL-33 interaction), NF-κB reporter assay in ST2L-expressing EL-4 cells, murine asthma model","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — direct binding demonstrated, functional block confirmed in vitro and in vivo","pmids":["17623648"],"is_preprint":false},{"year":2008,"finding":"IL-33 is constitutively and abundantly expressed in the nucleus of endothelial cells and epithelial cells in normal human tissues in vivo, establishing these cells as major sources and suggesting a dual role as an intracellular nuclear factor and extracellular alarmin.","method":"Human tissue microarrays, immunohistochemistry with monoclonal and polyclonal antibodies","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 — systematic tissue survey with multiple validated antibodies, widely cited and replicated","pmids":["18836528"],"is_preprint":false},{"year":2009,"finding":"Full-length IL-33(1-270) is biologically active and directly binds/activates ST2; caspase-1 cleaves IL-33 after Asp178 (not at Ser111 as previously proposed), resulting in IL-33 inactivation rather than activation. IL-33 is also a substrate for apoptotic caspase-3 at the same consensus motif (DGVD178G).","method":"In vitro caspase cleavage assays, ST2 binding assays, site determination by mass spectrometry, cellular activity assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with precise cleavage-site mapping and functional bioactivity assays","pmids":["19439663"],"is_preprint":false},{"year":2009,"finding":"Apoptotic caspases-3 and -7 (but not inflammatory caspases-1, -4, or -5) process IL-33, and this cleavage dramatically attenuates IL-33 bioactivity both in vitro and in vivo; caspase-dependent proteolysis acts as a switch to dampen IL-33's proinflammatory properties during apoptosis.","method":"In vitro caspase activity assays, ST2 binding assays, in vivo bioactivity models, caspase specificity panels","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with multiple caspases, confirmed in vivo, independently corroborates PMID 19439663","pmids":["19559631"],"is_preprint":false},{"year":2012,"finding":"Neutrophil serine proteases cathepsin G and elastase cleave full-length human IL-33(1-270) to generate mature bioactive forms IL-33(95-270), IL-33(99-270), and IL-33(109-270) with ~10-fold higher biological activity than full-length IL-33; these forms are produced by activated human neutrophils ex vivo and are active in vivo.","method":"In vitro protease cleavage, mass spectrometry cleavage-site mapping, neutrophil ex vivo assays, in vivo bronchoalveolar lavage model","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with precise site mapping confirmed ex vivo and in vivo","pmids":["22307629"],"is_preprint":false},{"year":2009,"finding":"IL-33 amplifies IL-13-induced polarization of alveolar and bone marrow-derived macrophages toward the alternatively activated (AAM) phenotype via ST2L; IL-13/IL-4Rα signaling is required for this effect by upregulating ST2L expression. AAM-derived CCL24 mediates downstream eosinophil recruitment.","method":"In vitro macrophage polarization assays, alveolar macrophage depletion, ST2-knockout mice, cytokine neutralization","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 2 — genetic (ST2-KO) and antibody-mediated epistasis with in vitro mechanistic follow-up","pmids":["19841166"],"is_preprint":false},{"year":2009,"finding":"IL-33 directly activates primary human mast cells to produce proinflammatory cytokines/chemokines via ST2L, and also accelerates in vitro maturation of CD34+ mast cell precursors.","method":"Primary human mast cell culture, cytokine ELISA, CD34+ precursor differentiation assay","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 2 — primary cell assays with ST2L blockade controls, widely replicated (419 citations)","pmids":["17675461"],"is_preprint":false},{"year":2008,"finding":"Human eosinophils express ST2 (mRNA and protein), and IL-33 stimulates eosinophil superoxide anion production, degranulation, survival, and IL-8 production as potently as IL-5; anti-ST2 antibody blocks these effects.","method":"RT-PCR, flow cytometry, superoxide assay, degranulation assay, ELISA, antibody blockade","journal":"The Journal of allergy and clinical immunology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal functional assays with receptor blockade, widely replicated (414 citations)","pmids":["18539196"],"is_preprint":false},{"year":2016,"finding":"IL-33/ST2 signaling is required for thermogenic licensing of brown and beige adipocytes during the perinatal period; in the absence of IL-33 or ST2, adipocytes fail to express correctly spliced Ucp1 mRNA and UCP1 protein, resulting in impaired uncoupled respiration and thermoregulation, despite normal adipocyte development.","method":"IL-33-KO and ST2-KO mice, RNA splicing analysis, UCP1 Western blot, metabolic/thermoregulation phenotyping","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with defined molecular phenotype (Ucp1 mis-splicing) and functional metabolic readout","pmids":["27453471"],"is_preprint":false},{"year":2018,"finding":"Nuclear IL-33 binds chromatin with ~10-fold lower intranuclear mobility than IL-1α (measured by FRAP); chromatin binding restrains necrosis-induced IL-33 release (slower, linear kinetics compared to truncated IL-33 or IL-1α) and IL-33 is released as a high-molecular-weight complex with histones that synergistically activates ST2-mediated signaling.","method":"FRAP live imaging, necrosis-induced release assays, size-exclusion fractionation, ST2-signaling reporter assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1-2 — FRAP quantification, biochemical fractionation, and functional synergy assay in one study","pmids":["30108214"],"is_preprint":false},{"year":2009,"finding":"IL-33 induces cutaneous fibrosis in an IL-33R (ST2)-dependent manner, requiring IL-13 production and eosinophils; bone marrow-derived eosinophils secrete IL-13 in response to IL-33 stimulation, identifying eosinophil-derived IL-13 as a downstream mediator of IL-33-induced fibrosis.","method":"Subcutaneous IL-33 administration, IL-13 knockout mice, ΔdblGATA eosinophil-deficient mice, bone marrow-derived eosinophil stimulation assays","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 2 — two independent genetic KO models with defined cellular and cytokine epistasis","pmids":["20042577"],"is_preprint":false},{"year":2017,"finding":"Nuclear FAK enhances IL-33 gene expression in squamous cell carcinoma cells; IL-33 associates with FAK in the nucleus and the FAK-IL-33 complex interacts with chromatin modifiers TAF9, WDR82, and BRD4 to promote NF-κB-driven CCL5 expression and immune evasion.","method":"Co-immunoprecipitation (nuclear FAK–IL-33 complex), ChIP, RNA-seq, shRNA knockdown, syngeneic tumor implantation","journal":"Science signaling","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP and ChIP evidence for nuclear complex; single lab but multiple methods","pmids":["29208683"],"is_preprint":false},{"year":2021,"finding":"FAK controls IL-33 gene expression by regulating chromatin accessibility at c-Jun/AP-1 motifs in the Il33 promoter/enhancer region; c-Jun binds the Il33 enhancer in a FAK kinase activity-dependent manner.","method":"ATAC-seq, RNA-seq, ChIP for c-Jun, FAK inhibition/overexpression","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 — ATAC-seq and ChIP provide mechanistic chromatin-level evidence; single lab","pmids":["33420223"],"is_preprint":false},{"year":2017,"finding":"IL-33 promotes colon cancer cell stemness through ST2-dependent activation of JNK/c-Jun signaling, which drives binding of c-Jun to promoters of core stem cell genes NANOG, NOTCH3, and OCT3/4; IL-33 also recruits macrophages to produce prostaglandin E2, further supporting stemness.","method":"ChIP (c-Jun at stem cell gene promoters), phospho-JNK assays, ST2 pathway inhibition, in vivo tumor models","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP and phosphoprotein assays with pathway validation; single lab","pmids":["28249897"],"is_preprint":false},{"year":2010,"finding":"IL-33 reduces macrophage foam cell formation via the ST2 receptor by decreasing modified LDL uptake (downregulating CD36), reducing cholesterol esterification (downregulating ACAT1), and enhancing cholesterol efflux (upregulating ApoE); ST2-deficient bone marrow-derived macrophages confirm ST2 is required.","method":"In vivo ApoE-/- atherosclerosis model, THP-1 and primary human macrophage foam cell assays, cholesterol efflux assays, gene expression, ST2-/- bone marrow-derived macrophages","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 2 — genetic (ST2-KO) and in vitro mechanistic data with defined molecular targets, in vivo confirmation","pmids":["20543107"],"is_preprint":false},{"year":2017,"finding":"IL-33 activates SOCS3 expression to inhibit the IL-17 receptor signaling pathway, thereby reducing proinflammatory cytokine production in sepsis; IL-33 KO mice show increased mortality in cecal ligation-puncture sepsis, and this phenotype is linked to unrestrained IL-17 signaling from γδT cells.","method":"IL-33-/- mouse CLP model, in vivo cytokine measurement, in vitro MEF knockdown of SOCS3, IL-17 pathway phosphoprotein assays","journal":"Cellular physiology and biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KO with defined downstream pathway; single lab","pmids":["28793286"],"is_preprint":false},{"year":2019,"finding":"Cell-intrinsic IL-33 (ST2-independent) in regulatory T cells maintains their suppressive function; IL-33-deficient Tregs show NF-κB–T-bet-dependent epigenetic reprogramming (increased chromatin accessibility at the Ifng locus) leading to elevated IFN-γ production that impairs Treg suppressive capacity.","method":"Conditional IL-33 KO in Tregs, ATAC-seq, intracellular IFN-γ flow cytometry, in vivo tumor suppression assays, T-bet/NF-κB epistasis","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 1-2 — epigenomic (ATAC-seq) plus genetic epistasis (T-bet, NF-κB, IFN-γ ablation) with in vivo functional validation","pmids":["31844326"],"is_preprint":false},{"year":2019,"finding":"IL-33 expressed in dendritic cells (CD11c+ cells) promotes perforin-2 expression on DCs; perforin-2 acts as a plasma membrane conduit for IL-33 export from DCs, facilitating IL-33-driven expansion of ST2+Foxp3+GATA3+ Treg cells and mucosal immunoregulation.","method":"Conditional IL-33 KO in CD11c+ cells, conditional perforin-2 KO, flow cytometry of Treg subsets, ex vivo DC stimulation assays","journal":"Science immunology","confidence":"Medium","confidence_rationale":"Tier 2 — conditional KOs with defined cellular phenotype; perforin-2 conduit mechanism is novel single-lab finding","pmids":["33188058"],"is_preprint":false},{"year":2019,"finding":"Cell-intrinsic IL-33 (ST2-independent) in pro-B and large precursor B cells regulates early B cell development; IL-33 deficiency leads to increased E2F targets/cell cycle genes and decreased p53 pathway activity, resulting in increased frequency of developing B cells via a cell-intrinsic mechanism.","method":"Mixed bone marrow chimeric mice, RNA-seq of WT vs IL-33-/- pro-B cells, ST2 expression analysis by RT-PCR and flow cytometry","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"Medium","confidence_rationale":"Tier 2 — chimeric mouse epistasis plus transcriptomic mechanistic analysis; single lab","pmids":["31391233"],"is_preprint":false},{"year":2021,"finding":"IL-33 activates mTORC1 in CD8+ T cells (evidenced by increased phospho-S6), and this mTORC1 activation drives upregulation of Glut1 and glycolytic enzymes, leading to increased glycolytic capacity (Warburg effect) and enhanced CD8+ T cell effector activation.","method":"Adoptive transfer experiments, phospho-S6 Western blot/flow cytometry, mTORC1 inhibitor rescue, glycolytic rate assay, Glut1 expression analysis","journal":"Immunology","confidence":"Medium","confidence_rationale":"Tier 2 — phosphoprotein assays with pharmacological inhibitor rescue and metabolic functional readout; single lab","pmids":["34411293"],"is_preprint":false},{"year":2022,"finding":"Thrombin directly cleaves IL-33 at specific amino acids R48 and R106 to generate a mature bioactive form; low-molecular-weight heparin (thrombin inhibitor) restrains type 2 immune responses in mice by inhibiting IL-33 cleavage.","method":"In vitro protease cleavage with site-directed mutagenesis, in vivo papain/fungus/HDM/OVA airway inflammation models with thrombin inhibitors","journal":"Allergy","confidence":"Medium","confidence_rationale":"Tier 1-2 — in vitro cleavage with site identification confirmed in multiple in vivo models; single lab","pmids":["34995358"],"is_preprint":false},{"year":2021,"finding":"IL-33 precedes IL-5 in regulating eosinophil commitment; IL-33 (via ST2) supports eosinophil maturation by driving systemic IL-5 production AND by expanding IL-5Rα-expressing precursor cells in bone marrow, establishing a two-step mechanism for eosinophilopoiesis.","method":"IL-33-KO and ST2-KO mice, IL-5 neutralization, in vitro bone marrow culture with IL-33/IL-5, IL-5 transgenic × ST2-KO crosses","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 2 — multiple genetic models with cytokine-neutralization epistasis","pmids":["27683753"],"is_preprint":false},{"year":2021,"finding":"GSK3β inhibition downstream of PI3K/Akt (induced by IL11 via STAT3) promotes epithelial IL-33 expression; IL11 is the most potent known inducer of IL33 in fibroblasts (38-fold upregulation), and STAT3 inhibition (but not MEK/ERK inhibition) prevents this induction.","method":"RNA-seq time course, STAT3 and MEK inhibitors, IL-33 protein quantification in primary human fibroblasts from kidney, lung, and skin","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological epistasis in multiple primary cell types; single lab","pmids":["36012165"],"is_preprint":false},{"year":2018,"finding":"Oxidized IL-33 (IL-33ox, non-ST2-binding form) forms a complex with RAGE and EGFR on airway epithelium, activating an ST2-independent pathway that impairs wound closure, increases mucus-producing cells, and induces epithelial remodeling mimicking COPD pathology.","method":"Co-immunoprecipitation of IL-33ox–RAGE–EGFR complex, in vitro epithelial damage assays, air-liquid interface models, single-cell RNA-seq, IL-33-neutralizing antibody reversal","journal":"The European respiratory journal","confidence":"High","confidence_rationale":"Tier 1-2 — complex identified by Co-IP, functional consequences in ALI models plus scRNA-seq mechanistic characterization, therapeutic reversal","pmids":["37442582"],"is_preprint":false},{"year":2023,"finding":"PLP (active vitamin B6) regulates IL-33 protein stability by reducing MDM2-mediated polyubiquitination of the IL-33 N-terminus, leading to increased proteasomal degradation of IL-33 and attenuation of type 2 inflammation; PDXK heterozygous mice (reduced PL→PLP conversion) show elevated lung IL-33 and worsened type 2 inflammation.","method":"In vivo PDXK heterozygous and MDM2 knockdown mouse models, ubiquitination assays, proteasome inhibitor rescue, IL-33 stability measurements","journal":"Cellular & molecular immunology","confidence":"Medium","confidence_rationale":"Tier 2 — ubiquitination assays with genetic mouse model confirmation; single lab","pmids":["37217797"],"is_preprint":false},{"year":2019,"finding":"IL-33 inactivates GSK-3β through an ST2-independent MyD88/TRAF6/RIP/PI3K/Akt signaling pathway in PC-12 cells, and neutralizes Aβ1-42-induced Akt inactivation and GSK-3β activation.","method":"siRNA knockdown of MyD88, TRAF6, RIP, PI3K; Western blot for Akt and GSK-3β phosphorylation","journal":"Heliyon","confidence":"Medium","confidence_rationale":"Tier 2 — systematic siRNA epistasis; single lab, single cell line","pmids":["30533546"],"is_preprint":false},{"year":2021,"finding":"Asthma-associated SNP rs1888909 within a 5 kb enhancer-blocking element at the IL33 locus alters binding of the transcription factor OCT-1 (POU2F1) in an allele-specific manner, regulating IL33 gene expression in airway epithelial cells and IL-33 protein levels in plasma.","method":"Chromatin conformation capture (3C), in vivo and in vitro enhancer-blocking assays, allele-specific expression analysis (RNA-seq), OCT-1 binding EMSA","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1-2 — 3C looping, functional enhancer assays, and allele-specific OCT-1 binding with human tissue validation","pmids":["34675193"],"is_preprint":false},{"year":2017,"finding":"A rare splice-acceptor variant in IL33 (rs146597587-C) causes intron retention with a premature stop codon, truncating the last 66 amino acids; the truncated IL-33 protein has normal intracellular localization but neither binds ST2 nor activates ST2-expressing cells, confirming the C-terminal IL-1-like domain is essential for receptor binding and activity.","method":"Whole-genome sequencing, allele-specific RNA-seq, recombinant truncated IL-33 binding and cell activation assays, cellular localization imaging","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 1-2 — recombinant protein binding assay, population-scale allele-specific expression, and cellular localization in one study","pmids":["28273074"],"is_preprint":false},{"year":2019,"finding":"IL-33 reduces CLDN1 (claudin-1) expression in keratinocytes through the ERK/STAT3 pathway; STAT3 directly binds the CLDN1 promoter to suppress transcription, leading to impaired skin barrier function.","method":"MAPK inhibitors, siRNA knockdown, EMSA/EMSA (STAT3 binding to CLDN1 promoter), TEER and FITC-dextran flux assays","journal":"Journal of dermatological science","confidence":"Medium","confidence_rationale":"Tier 2 — EMSA confirms direct STAT3–promoter binding; pathway confirmed by inhibitors and siRNA; single lab","pmids":["29534857"],"is_preprint":false},{"year":2022,"finding":"P2Y13 receptor (a purinergic GPCR) acts as a gatekeeper of IL-33 release from airway epithelial cells; aeroallergen or virus exposure triggers extracellular ADP/ATP release that activates P2Y13-R, inducing nuclear-to-cytoplasmic translocation and subsequent secretion of IL-33; genetic deletion or pharmacological antagonism of P2Y13 ablates this response.","method":"P2Y13-R knockout mice, pharmacological antagonism, immunohistochemistry for nuclear-to-cytoplasmic translocation, ELISA, experimental asthma models","journal":"American journal of respiratory and critical care medicine","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KO plus pharmacological confirmation with mechanistic translocation readout; single lab","pmids":["34860143"],"is_preprint":false},{"year":2019,"finding":"Glutaredoxin-1 (Glrx) controls NF-κB-dependent IL-33 induction in macrophages by maintaining TRAF6 in its de-glutathionylated (active) state; Glrx knockdown impairs TRAF6 de-glutathionylation, blocks IKKβ/NF-κB activation, and reduces LPS-induced IL-33 mRNA; paracrine IL-33 in turn induces Glrx, creating a feed-forward loop.","method":"Glrx KO mice, siRNA knockdown, S-glutathionylation assay of TRAF6, NF-κB reporter, chromatin IP confirming NF-κB binding to Il33 locus","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP, post-translational modification assay, and genetic KO; single lab","pmids":["30682073"],"is_preprint":false},{"year":2022,"finding":"IL-33 signaling in microglia promotes synaptic refinement by inducing an AP-1/FOS-driven gene expression program including the scavenger receptor MARCO; MARCO promotes synapse engulfment and CNS-specific IL-33 deletion causes excess excitatory synapses and seizure susceptibility.","method":"IL-33 supraphysiological CNS delivery, microglial enhancer landscape (ATAC-seq/ChIP), CNS-specific IL-33 KO mice, Marco-KO mice, synapse counting, EEG seizure monitoring","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 1-2 — epigenomic profiling, two independent genetic KO models, and functional neurological readouts","pmids":["36520518"],"is_preprint":false},{"year":2020,"finding":"Staphylococcus aureus second immunoglobulin-binding protein (Sbi) is the predominant virulence factor that drives rapid release of constitutively stored IL-33 from human keratinocytes, independently of Toll-like receptor signaling and independently of necrosis; this IL-33 release is essential for the type 2 immune response to S. aureus in vivo.","method":"FPLC fractionation, mass spectrometry, S. aureus Sbi mutant strains, recombinant Sbi expression, in vivo NC/Tnd mouse model with IL-33 blockade","journal":"The Journal of allergy and clinical immunology","confidence":"High","confidence_rationale":"Tier 1-2 — protein identification by MS, confirmed with loss-of-function mutant bacteria and in vivo validation","pmids":["33011245"],"is_preprint":false}],"current_model":"IL-33 is a dual-function nuclear cytokine constitutively stored in the chromatin of endothelial and epithelial cells via an N-terminal homeodomain-like HTH motif; upon cellular damage or stress, full-length IL-33 is released (regulated by chromatin binding kinetics and conduits such as perforin-2) and signals through the ST2/IL-1RAcP co-receptor complex to activate NF-κB and MAPK pathways, driving TH2, ILC2, mast cell, and eosinophil responses, while its bioactivity is modulated post-translationally by neutrophil elastase/cathepsin G (generating hyperactive ~10-fold more potent mature forms), apoptotic caspases-3/7 (inactivating cleavage), thrombin (activating cleavage at R48/R106), MDM2-mediated ubiquitination (stability regulation), oxidation to a non-ST2-binding form (IL-33ox) that instead activates a RAGE/EGFR pathway, and nuclear sequestration by chromatin; intranuclear IL-33 also exerts ST2-independent cell-intrinsic functions in Treg stability, B cell development, and transcriptional regulation through interactions with FAK, chromatin modifiers (TAF9, WDR82, BRD4), and AP-1/c-Jun."},"narrative":{"teleology":[{"year":2005,"claim":"Identification of IL-33 as the functional ligand for the orphan receptor ST2 established that the IL-1 family includes a potent TH2-polarizing cytokine, resolving a long-standing gap in ST2 biology.","evidence":"Receptor-ligand binding assays, NF-κB reporter assays, and in vivo cytokine measurement in mice","pmids":["16286016"],"confidence":"High","gaps":["Mechanism of IL-33 release from cells was unknown","Whether IL-33 required processing for activity was unresolved","Structural basis of IL-33–ST2 interaction not determined"]},{"year":2006,"claim":"Discovery that IL-33 is a chromatin-associated nuclear factor (NF-HEV) with transcriptional repressor activity revealed its dual identity as both an intracellular regulator and an extracellular cytokine.","evidence":"Immunostaining, live-cell imaging of chromatin co-localization, and transcriptional repressor assays","pmids":["17185418"],"confidence":"High","gaps":["Nuclear targets of IL-33 repression were uncharacterized","Whether chromatin binding regulates IL-33 release was unknown"]},{"year":2007,"claim":"Identification of IL-1RAcP as an obligate co-receptor for ST2 and of soluble ST2 as a decoy receptor defined the complete receptor architecture and a natural brake on IL-33 signaling.","evidence":"Co-immunoprecipitation, dominant-negative IL-1RAcP, direct sST2–IL-33 binding assays, and in vivo functional models","pmids":["17675517","17623648"],"confidence":"High","gaps":["Stoichiometry of the ternary signaling complex was not resolved","Mechanisms governing sST2 shedding were not defined"]},{"year":2008,"claim":"Tissue-level surveys established endothelial and epithelial cells as constitutive nuclear reservoirs of IL-33, and functional studies showed IL-33 directly activates eosinophils and mast cells via ST2, defining the key cellular effectors of the pathway.","evidence":"Human tissue microarray immunohistochemistry; primary eosinophil functional assays with ST2 blockade; primary mast cell cytokine and maturation assays","pmids":["18836528","18539196","17675461"],"confidence":"High","gaps":["Release mechanism from intact cells was still undefined","Relative contributions of mast cells vs. eosinophils in vivo unclear"]},{"year":2009,"claim":"Reconstitution of caspase cleavage resolved the critical question of how apoptosis silences IL-33: caspases-3/7 inactivate full-length IL-33 rather than activating it, distinguishing IL-33 from IL-1β/IL-18 and establishing apoptosis as an anti-inflammatory checkpoint for this alarmin.","evidence":"In vitro caspase cleavage with mass spectrometry site mapping, ST2 binding assays, and in vivo bioactivity models","pmids":["19439663","19559631"],"confidence":"High","gaps":["Whether other proteases generate active forms was unknown","In vivo relevance of caspase-mediated inactivation during infection not tested"]},{"year":2009,"claim":"Downstream effector biology was elaborated: IL-33 amplifies alternative macrophage activation via IL-13/ST2L crosstalk, drives eosinophil-dependent cutaneous fibrosis through IL-13, and directly induces mast cell cytokine production, establishing IL-33 as a master upstream regulator of type 2 tissue inflammation.","evidence":"Macrophage polarization with ST2-KO mice; ΔdblGATA eosinophil-deficient and IL-13-KO mice; bone marrow eosinophil stimulation assays","pmids":["19841166","20042577"],"confidence":"High","gaps":["Whether IL-33 drives fibrosis independently of eosinophils in other tissues was unknown","Direct transcriptional targets in macrophages were not mapped"]},{"year":2012,"claim":"Discovery that neutrophil serine proteases cathepsin G and elastase generate hyperactive (~10-fold more potent) mature IL-33 forms answered how full-length IL-33 is activated in inflammatory microenvironments without inflammasome processing.","evidence":"In vitro protease cleavage with mass spectrometry site identification, neutrophil ex vivo processing, and in vivo bronchoalveolar lavage","pmids":["22307629"],"confidence":"High","gaps":["Whether mast cell proteases similarly process IL-33 was untested","Relative contribution of each mature form in disease settings was unclear"]},{"year":2016,"claim":"IL-33/ST2 signaling was shown to license thermogenic gene expression (correct Ucp1 splicing) in perinatal adipocytes, extending IL-33 biology beyond immunity into metabolic physiology.","evidence":"IL-33-KO and ST2-KO mice with Ucp1 splicing analysis, UCP1 protein quantification, and thermoregulation phenotyping","pmids":["27453471"],"confidence":"High","gaps":["Mechanism by which IL-33 regulates Ucp1 splicing was not identified","Source of IL-33 in the adipose niche was not defined"]},{"year":2017,"claim":"Nuclear IL-33 was found to form a complex with FAK and chromatin modifiers TAF9, WDR82, and BRD4, driving NF-κB-dependent CCL5 transcription in squamous cell carcinoma, revealing a direct transcriptional co-regulatory function and linking nuclear IL-33 to immune evasion.","evidence":"Nuclear Co-IP of FAK–IL-33 complex, ChIP at target promoters, RNA-seq, shRNA knockdown, syngeneic tumor models","pmids":["29208683"],"confidence":"Medium","gaps":["Whether the FAK–IL-33 nuclear complex exists outside squamous carcinoma contexts is untested","Direct DNA-binding contribution of IL-33 versus scaffolding role not distinguished","Awaits independent replication"]},{"year":2017,"claim":"A rare loss-of-function splice variant (rs146597587-C) truncating the C-terminal IL-1-like domain confirmed that this domain is absolutely required for ST2 binding, providing human genetic validation of the structure–function relationship.","evidence":"Whole-genome sequencing, allele-specific RNA-seq, recombinant truncated IL-33 binding and activation assays","pmids":["28273074"],"confidence":"High","gaps":["Structural basis of C-terminal domain–ST2 interaction at atomic resolution not resolved","Phenotypic consequence in carriers not fully characterized"]},{"year":2018,"claim":"FRAP and biochemical fractionation demonstrated that chromatin tethering slows IL-33 release kinetics during necrosis and that IL-33 exits as a histone-bound complex that synergistically enhances ST2 signaling, integrating the nuclear and alarmin functions into a unified release-and-signal mechanism.","evidence":"FRAP live imaging, necrosis-induced release kinetics, size-exclusion chromatography, ST2 reporter assays","pmids":["30108214"],"confidence":"High","gaps":["Identity of the histone partners in the complex not determined","Whether histone association affects half-life in vivo was untested"]},{"year":2018,"claim":"Discovery that oxidized IL-33 (IL-33ox) loses ST2-binding capacity but gains the ability to signal through a RAGE/EGFR complex revealed a second, ST2-independent signaling axis with distinct pathological consequences in airway epithelial remodeling.","evidence":"Co-IP of IL-33ox–RAGE–EGFR, air-liquid interface epithelial models, single-cell RNA-seq, antibody reversal","pmids":["37442582"],"confidence":"High","gaps":["Structural basis of IL-33ox selectivity for RAGE/EGFR over ST2 unknown","Relative abundance of IL-33ox vs. reduced IL-33 in disease tissues not quantified"]},{"year":2019,"claim":"Conditional knockout studies revealed that cell-intrinsic nuclear IL-33 maintains Treg suppressive function by preventing NF-κB–T-bet-driven epigenetic reprogramming at the Ifng locus, establishing a major ST2-independent intracellular role in immune homeostasis.","evidence":"Conditional IL-33 KO in Tregs, ATAC-seq of chromatin accessibility, intracellular cytokine flow cytometry, in vivo tumor suppression, T-bet/NF-κB epistasis","pmids":["31844326"],"confidence":"High","gaps":["Molecular mechanism by which nuclear IL-33 restrains T-bet/NF-κB access is not defined","Whether this applies to human Tregs is untested"]},{"year":2019,"claim":"Cell-intrinsic IL-33 was shown to regulate early B cell development in a ST2-independent manner, with IL-33 deficiency increasing E2F/cell cycle programs and expanding developing B cell populations, broadening the nuclear functions beyond Treg biology.","evidence":"Mixed bone marrow chimeras, RNA-seq of WT vs. IL-33−/− pro-B cells, ST2 expression analysis","pmids":["31391233"],"confidence":"Medium","gaps":["Direct chromatin targets of IL-33 in B cell precursors not identified","Protein-level mechanism (scaffolding vs. transcriptional) unclear","Single-lab finding"]},{"year":2019,"claim":"Perforin-2 was identified as a conduit for IL-33 export from dendritic cells, providing a non-necrotic secretory mechanism and linking IL-33 release to regulated mucosal Treg expansion.","evidence":"Conditional IL-33 and perforin-2 KO in CD11c+ cells, flow cytometry of Treg subsets, ex vivo DC stimulation","pmids":["33188058"],"confidence":"Medium","gaps":["Whether perforin-2 is the sole non-lytic export route is unknown","Structural basis of IL-33–perforin-2 interaction not determined","Single-lab finding"]},{"year":2021,"claim":"Asthma-associated SNP rs1888909 was shown to alter OCT-1 binding at an IL33 enhancer element, providing a mechanistic basis for genetic regulation of IL-33 expression and disease risk.","evidence":"Chromatin conformation capture (3C), enhancer-blocking assays, allele-specific expression, OCT-1 EMSA","pmids":["34675193"],"confidence":"High","gaps":["Full repertoire of transcription factors regulated by this enhancer not mapped","Whether additional GWAS SNPs operate through the same element is unknown"]},{"year":2022,"claim":"Thrombin was identified as a novel activating protease for IL-33 (cleaving at R48 and R106), adding the coagulation cascade to the regulatory protease network and showing that anticoagulants can restrain type 2 immunity by blocking IL-33 maturation.","evidence":"In vitro cleavage with site-directed mutagenesis, multiple in vivo airway inflammation models with thrombin inhibitors","pmids":["34995358"],"confidence":"Medium","gaps":["Relative potency of thrombin-generated forms vs. neutrophil protease-generated forms not compared","In vivo evidence of thrombin-dependent IL-33 cleavage at steady state lacking"]},{"year":2022,"claim":"IL-33 in microglia was shown to drive an AP-1/FOS transcriptional program including MARCO upregulation that promotes synapse engulfment, connecting IL-33 to CNS synaptic refinement and seizure susceptibility.","evidence":"ATAC-seq/ChIP of microglial enhancers, CNS-specific IL-33 KO and Marco-KO mice, synapse quantification, EEG seizure monitoring","pmids":["36520518"],"confidence":"High","gaps":["Whether astrocyte- or neuron-derived IL-33 differentially contributes is untested","Temporal window of IL-33-dependent synaptic pruning not defined"]},{"year":2023,"claim":"MDM2-mediated polyubiquitination of the IL-33 N-terminus was identified as a degradation pathway regulated by vitamin B6 (PLP), establishing a metabolic checkpoint for IL-33 protein stability and type 2 inflammation.","evidence":"Ubiquitination assays, proteasome inhibitor rescue, PDXK heterozygous mouse model with elevated lung IL-33","pmids":["37217797"],"confidence":"Medium","gaps":["Specific ubiquitinated lysine residues not mapped","Whether MDM2 regulation is relevant in non-pulmonary tissues untested","Single-lab finding"]},{"year":null,"claim":"Key unresolved questions include the atomic-resolution structure of the IL-33–ST2–IL-1RAcP ternary complex, the precise molecular mechanism by which nuclear IL-33 restrains T-bet/NF-κB chromatin remodeling in Tregs, the full spectrum of non-lytic secretion pathways beyond perforin-2, and whether IL-33ox/RAGE/EGFR signaling is a general tissue damage pathway or restricted to airway epithelium.","evidence":"","pmids":[],"confidence":"High","gaps":["Atomic structure of signaling complex not solved","Nuclear mechanism of Treg stabilization molecularly undefined","Non-lytic secretion pathway incompletely characterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[0,5,7,30]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[1,14]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,26]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[1,4,12,14]},{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[1,12]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,5,7,12]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,8,9,10,13,19,24]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,2,3,16,26,28]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[16,26,29]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[5,6,7,23,27]}],"complexes":["ST2/IL-1RAcP receptor complex (extracellular ligand)","FAK–IL-33–TAF9–WDR82–BRD4 nuclear complex","IL-33–histone release complex","IL-33ox–RAGE–EGFR complex"],"partners":["IL1RL1","IL1RAP","PTK2","TAF9","WDR82","BRD4","AGER","EGFR"],"other_free_text":[]},"mechanistic_narrative":"IL-33 is a dual-function alarmin cytokine that operates both as a chromatin-associated nuclear factor and as an extracellular ligand for the ST2/IL-1RAcP receptor complex, orchestrating type 2 immunity, tissue homeostasis, and damage responses across epithelial, endothelial, and immune compartments. Full-length IL-33 is constitutively stored in the nucleus of endothelial and epithelial cells, tethered to chromatin via an N-terminal homeodomain-like HTH motif; upon tissue damage it is released—often as a high-molecular-weight histone complex—and signals through ST2 to activate NF-κB and MAPK cascades that drive TH2, ILC2, mast cell, and eosinophil effector programs [PMID:16286016, PMID:17185418, PMID:18836528, PMID:30108214]. Bioactivity is tightly regulated by post-translational processing: neutrophil elastase and cathepsin G generate hyperactive mature forms (~10-fold more potent), thrombin cleaves at R48/R106 to produce additional active species, apoptotic caspases-3/7 inactivate IL-33, and oxidation converts it to a non-ST2-binding form (IL-33ox) that instead engages a RAGE/EGFR pathway driving epithelial remodeling [PMID:22307629, PMID:19559631, PMID:34995358, PMID:37442582]. Beyond its extracellular cytokine role, cell-intrinsic nuclear IL-33 maintains regulatory T cell suppressive identity by restraining NF-κB–T-bet–driven IFN-γ epigenetic reprogramming and regulates early B cell development through ST2-independent mechanisms [PMID:31844326, PMID:31391233]."},"prefetch_data":{"uniprot":{"accession":"O95760","full_name":"Interleukin-33","aliases":["Interleukin-1 family member 11","IL-1F11","Nuclear factor from high endothelial venules","NF-HEV"],"length_aa":270,"mass_kda":30.8,"function":"Cytokine that binds to and signals through the IL1RL1/ST2 receptor which in turn activates NF-kappa-B and MAPK signaling pathways in target cells (PubMed:16286016, PubMed:19841166). Involved in the maturation of Th2 cells inducing the secretion of T-helper type 2-associated cytokines (PubMed:17853410, PubMed:18836528). Also involved in activation of mast cells, basophils, eosinophils and natural killer cells (PubMed:17853410, PubMed:18836528). Acts as an enhancer of polarization of alternatively activated macrophages (PubMed:19841166). Acts as a chemoattractant for Th2 cells, and may function as an 'alarmin', that amplifies immune responses during tissue injury (PubMed:17853410, PubMed:18836528). Induces rapid UCP2-dependent mitochondrial rewiring that attenuates the generation of reactive oxygen species and preserves the integrity of Krebs cycle required for persistent production of itaconate and subsequent GATA3-dependent differentiation of inflammation-resolving alternatively activated macrophages (By similarity) In quiescent endothelia the uncleaved form is constitutively and abundantly expressed, and acts as a chromatin-associated nuclear factor with transcriptional repressor properties, it may sequester nuclear NF-kappaB/RELA, lowering expression of its targets (PubMed:21734074). This form is rapidely lost upon angiogenic or pro-inflammatory activation (PubMed:18787100)","subcellular_location":"Nucleus; Chromosome; Cytoplasm; Cytoplasmic vesicle, secretory vesicle; Secreted","url":"https://www.uniprot.org/uniprotkb/O95760/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/IL33","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/IL33","total_profiled":1310},"omim":[{"mim_id":"620492","title":"MEDIATOR COMPLEX SUBUNIT 31; MED31","url":"https://www.omim.org/entry/620492"},{"mim_id":"608678","title":"INTERLEUKIN 33; IL33","url":"https://www.omim.org/entry/608678"},{"mim_id":"605658","title":"INTERLEUKIN 25; IL25","url":"https://www.omim.org/entry/605658"},{"mim_id":"605103","title":"NEUROMEDIN U; NMU","url":"https://www.omim.org/entry/605103"},{"mim_id":"604672","title":"CD209 ANTIGEN; CD209","url":"https://www.omim.org/entry/604672"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Vesicles","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"urinary bladder","ntpm":114.2}],"url":"https://www.proteinatlas.org/search/IL33"},"hgnc":{"alias_symbol":["DVS27","DKFZp586H0523","NF-HEV","IL1F11"],"prev_symbol":["C9orf26"]},"alphafold":{"accession":"O95760","domains":[{"cath_id":"-","chopping":"31-65_78-87","consensus_level":"medium","plddt":51.3438,"start":31,"end":87},{"cath_id":"2.80.10.50","chopping":"117-267","consensus_level":"high","plddt":85.28,"start":117,"end":267}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O95760","model_url":"https://alphafold.ebi.ac.uk/files/AF-O95760-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O95760-F1-predicted_aligned_error_v6.png","plddt_mean":66.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=IL33","jax_strain_url":"https://www.jax.org/strain/search?query=IL33"},"sequence":{"accession":"O95760","fasta_url":"https://rest.uniprot.org/uniprotkb/O95760.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O95760/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O95760"}},"corpus_meta":[{"pmid":"18613828","id":"PMC_18613828","title":"IL-1, 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[et al.]","url":"https://pubmed.ncbi.nlm.nih.gov/19763788","citation_count":114,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"25595648","id":"PMC_25595648","title":"Increased IL-33 expression in chronic obstructive pulmonary disease.","date":"2015","source":"American journal of physiology. 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immunology","url":"https://pubmed.ncbi.nlm.nih.gov/18539196","citation_count":414,"is_preprint":false,"source_track":"gene2pubmed"}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":50602,"output_tokens":8665,"usd":0.140891},"stage2":{"model":"claude-opus-4-6","input_tokens":12564,"output_tokens":3901,"usd":0.240517},"total_usd":0.816506,"stage1_batch_id":"msgbatch_01DzrsgVgYngY1hvM3DU1yF2","stage2_batch_id":"msgbatch_01KA9b7iRzKFdhoBUT7vCvSe","note":"batch pricing = 50% of standard","round2_stage1":{"model":"claude-sonnet-4-6","input_tokens":64211,"output_tokens":8514,"usd":0.160171},"round2_rules_fired":"R3","round2_stage2":{"model":"claude-opus-4-6","input_tokens":12647,"output_tokens":4802,"usd":0.274927}},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2008,\n      \"finding\": \"IL-33 binds to the orphan IL-1 family receptor T1/ST2 and requires IL-1RAcP as an accessory protein to form the functional receptor complex, activating downstream signaling similar to other IL-1 family members.\",\n      \"method\": \"Receptor binding studies and review of signaling pathway data\",\n      \"journal\": \"Immunological reviews\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — replicated across multiple labs, foundational receptor identification widely confirmed\",\n      \"pmids\": [\"18613828\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"IL-33 localizes constitutively to the nucleus of endothelial, epithelial, and fibroblast-like cells via a chromatin-binding N-terminal domain; nuclear IL-33 is retained by chromatin binding and released more slowly than truncated IL-33 lacking this domain, as demonstrated by FRAP showing ~10-fold slower intranuclear mobility of full-length IL-33 versus truncated IL-33.\",\n      \"method\": \"Fluorescence recovery after photobleaching (FRAP), overexpression in epithelial cells, necrosis-induced release assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct live-imaging with functional consequence; multiple orthogonal methods in one study\",\n      \"pmids\": [\"30108214\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"IL-33 and histones are released together as a high-molecular-weight complex following membrane dissolution, and this complex synergistically activates ST2-receptor-mediated signaling, indicating chromatin binding post-translationally regulates IL-33 bioactivity.\",\n      \"method\": \"Necrosis-induced release assay, biochemical fractionation, receptor-mediated signaling assay\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods, functional validation of complex activity\",\n      \"pmids\": [\"30108214\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"IL-33 signaling through ST2 licenses brown and beige adipocytes for uncoupled respiration during the perinatal period by controlling appropriate splicing of Ucp1 mRNA; in the absence of IL-33 or ST2, UCP1 protein is absent despite normal adipocyte development.\",\n      \"method\": \"IL-33 and ST2 knockout mouse models, UCP1 protein and mRNA analysis, thermoregulation assays\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic KO with specific mechanistic phenotype (splicing of Ucp1), replicated with two independent KO lines\",\n      \"pmids\": [\"27453471\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Nuclear FAK interacts directly with IL-33 in the nucleus of squamous cell carcinoma cells, and the FAK-IL-33 complex associates with chromatin modifiers and transcriptional regulators (TAF9, WDR82, BRD4) to promote NF-κB-dependent CCL5 expression, mediating tumor immune evasion.\",\n      \"method\": \"Co-immunoprecipitation, nuclear fractionation, genetic depletion of FAK/IL-33/sST2 in syngeneic mouse tumor models\",\n      \"journal\": \"Science signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP showing FAK-IL-33 nuclear complex, in vivo functional validation\",\n      \"pmids\": [\"29208683\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"FAK controls chromatin accessibility at the Il33 gene promoter/enhancer region through AP-1/c-Jun motifs; nuclear FAK kinase activity promotes c-Jun binding to the Il33 enhancer, driving IL-33 gene expression.\",\n      \"method\": \"ATAC-seq, RNA-seq, chromatin immunoprecipitation (ChIP), FAK kinase-dead mutants\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal genomic methods with mutagenesis\",\n      \"pmids\": [\"33420223\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"IL-33 has a cell-intrinsic, ST2-independent nuclear function in pro-B and large precursor B cells that regulates their fitness; IL-33 deficiency leads to increased B cell progenitor frequency via a cell-intrinsic mechanism, with a transcriptional profile showing altered E2F/cell cycle and p53 pathways, independent of ST2 expression.\",\n      \"method\": \"Mixed bone marrow chimeric mice, RNA sequencing of wild-type vs. IL-33-deficient pro-B cells, flow cytometry\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic KO with cell-intrinsic rescue experiment and RNA-seq mechanistic characterization\",\n      \"pmids\": [\"31391233\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"IL-33 has a cell-intrinsic role in Treg cell functional stability that is independent of ST2; IL-33-deficient Tregs show increased chromatin accessibility at the Ifng locus and elevated IFN-γ production via an NF-κB-T-bet-dependent mechanism, impairing their suppressive function.\",\n      \"method\": \"IL-33-deficient Treg-specific knockouts, epigenetic profiling (chromatin accessibility), in vivo tumor models, IFN-γ ablation rescue\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods, epistasis demonstrated by IFN-γ ablation rescue\",\n      \"pmids\": [\"31844326\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"IL-33 signaling through ST2 on macrophages facilitates a reparative metabolic program; cardiac allografts lacking IL-33 displayed accelerated vascular occlusion due to local augmentation of proinflammatory iNOS+ macrophages, demonstrating that graft-derived IL-33 directly restrains macrophage proinflammatory activation.\",\n      \"method\": \"IL-33-deficient cardiac transplant mouse model, local IL-33 delivery, macrophage phenotyping\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic KO with defined cellular phenotype and rescue by local IL-33 delivery\",\n      \"pmids\": [\"32644975\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Oxidized IL-33 (IL-33ox), which cannot bind ST2, forms a complex with RAGE and EGFR on airway epithelial cells, activating an ST2-independent pathway that impairs epithelial wound closure and induces mucus-producing cell expansion, replicating COPD pathogenic epithelial traits.\",\n      \"method\": \"In vitro epithelial damage assays, air-liquid interface cultures, bulk and single-cell RNA sequencing, IL-33-neutralizing antibody, transcriptomic analysis of COPD patient airways\",\n      \"journal\": \"The European respiratory journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — complex formation demonstrated, ST2-independence validated, multiple orthogonal methods\",\n      \"pmids\": [\"37442582\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"IL-33 activates core stem cell genes (NANOG, NOTCH3, OCT3/4) in colon cancer cells via the ST2 signaling pathway, inducing phosphorylation of JNK and enhanced c-Jun binding to stem cell gene promoters.\",\n      \"method\": \"IL-33 administration and overexpression in murine colon cancer models, ChIP for c-Jun binding, JNK phosphorylation assays\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — mechanistic pathway placement with ChIP and phosphorylation data, single lab\",\n      \"pmids\": [\"28249897\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"IL-33 signals through ST2 to reduce macrophage foam cell formation by decreasing acetylated and oxidized LDL uptake (via reduced CD36 expression), reducing intracellular cholesterol esterification, and enhancing cholesterol efflux (via increased ApoE); ST2-deficient bone marrow-derived macrophages lose this response.\",\n      \"method\": \"THP-1 cells and primary human macrophages in vitro, ST2-/- bone marrow-derived macrophages, ApoE-/- mouse atherosclerosis model, gene expression analysis\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ST2-/- genetic validation plus in vitro mechanistic gene expression analysis and in vivo model\",\n      \"pmids\": [\"20543107\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"IL-33-induced cutaneous fibrosis requires IL-13 and eosinophils; bone marrow-derived eosinophils secrete IL-13 in response to IL-33 stimulation, and eosinophil-derived IL-13 mediates fibrosis downstream of IL-33 signaling.\",\n      \"method\": \"IL-13 knockout mice, delta dblGATA eosinophil-deficient mice, bone marrow-derived eosinophil stimulation assay, subcutaneous IL-33 administration\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — dual genetic KO epistasis plus in vitro mechanistic validation\",\n      \"pmids\": [\"20042577\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"IL-33 signals through ST2-MyD88-STAT1 axis to induce costimulatory molecule expression on myeloid dendritic cells; MyD88 is required for IL-33-mediated increase in mDC number and upregulation of costimulatory molecules.\",\n      \"method\": \"Systemic rIL-33 administration in tumor-bearing mice, MyD88-deficient cells, STAT1 analysis, ST2 receptor requirement validation\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — genetic requirement for MyD88 demonstrated, pathway components identified\",\n      \"pmids\": [\"28011934\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"IL-33 down-regulates claudin-1 (CLDN1) expression in keratinocytes through activation of ERK and STAT3, with STAT3 directly binding to the CLDN1 promoter to suppress its transcription, leading to impaired barrier function.\",\n      \"method\": \"Normal human epidermal keratinocytes and skin equivalent models, MAPK inhibitors, siRNA knockdown, EMSA for STAT3 binding, TEER and FITC-dextran flux barrier assays\",\n      \"journal\": \"Journal of dermatological science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — EMSA demonstrates direct STAT3 promoter binding, functional barrier readout, siRNA validation\",\n      \"pmids\": [\"29534857\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"IL-33 activates mTORC1 in CD8+ T cells, promoting glucose transporter 1 (Glut1) expression and glycolytic enzyme expression via mTORC1, leading to enhanced aerobic glucose metabolism (Warburg effect) and increased effector T cell activation; mTORC1 inhibitors suppress this IL-33-induced activation.\",\n      \"method\": \"In vitro CD8+ T cell stimulation, p-S6 phosphorylation assay, mTORC1 inhibitor treatment, glycolytic rate assay, glucose uptake and lactate production measurements, LCMV infection in vivo model\",\n      \"journal\": \"Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological inhibition of mTORC1 with functional rescue, in vitro and in vivo validation\",\n      \"pmids\": [\"34411293\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"IL-33 secretion by myeloid dendritic cells is facilitated by perforin-2, which acts as a plasma membrane conduit; deletion of perforin-2 in DCs blocks IL-33 export and the proliferative expansion of ST2+Foxp3+ Treg cells, linking IL-33 secretion mechanism to mucosal immunoregulation.\",\n      \"method\": \"Conditional deletion of IL-33 in CD11c+ cells, perforin-2-deficient DC experiments, Foxp3+ Treg flow cytometry\",\n      \"journal\": \"Science immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — conditional genetic deletion with defined cellular and molecular phenotype\",\n      \"pmids\": [\"33188058\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"IL-33 released from damaged airway epithelium is controlled by P2Y13 receptor signaling; aeroallergen exposure induces extracellular ADP/ATP that activates P2Y13-R, triggering nuclear-to-cytoplasmic translocation and release of IL-33; genetic deletion or pharmacological antagonism of P2Y13 abrogates IL-33 release.\",\n      \"method\": \"P2Y13-R genetic deletion mice, pharmacological antagonists, immunohistochemistry for nuclear-to-cytoplasmic translocation, ELISA, allergen and rhinovirus mouse models\",\n      \"journal\": \"American journal of respiratory and critical care medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic deletion plus pharmacological validation, multiple disease models, mechanistic link to nuclear translocation\",\n      \"pmids\": [\"34860143\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Thrombin directly cleaves IL-33 at specific amino acid residues (R48 and R106) to generate a mature, bioactive form with potent biological activity; low-molecular-weight heparin and bivalirudin (thrombin inhibitors) reduce type 2 immune responses by preventing IL-33 cleavage and ILC2 activation.\",\n      \"method\": \"In vitro cleavage assay identifying specific cleavage sites, in vivo papain/HDM/OVA mouse models with thrombin inhibitor treatment, ILC2 functional assays, clinical plasma TATc correlation\",\n      \"journal\": \"Allergy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct in vitro cleavage assay with site identification, in vivo validation with pharmacological inhibitors\",\n      \"pmids\": [\"34995358\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"A rare splice-acceptor loss-of-function variant in IL33 (rs146597587-C) produces a truncated IL-33 protein that has normal intracellular localization but neither binds IL-33R/ST2 nor activates ST2-expressing cells, demonstrating that the C-terminal domain is required for receptor binding and signaling.\",\n      \"method\": \"Functional characterization of truncated IL-33 protein using ST2 binding assay and cell activation assay, whole-genome sequencing, RNA sequencing for allele-specific expression\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct in vitro functional assay (binding and activation) with genetic variant characterization\",\n      \"pmids\": [\"28273074\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"IL-33 promotes microglial synapse engulfment during postnatal brain development by inducing the pattern recognition receptor MARCO; IL-33 alters the microglial enhancer landscape and AP-1/FOS transcription factor binding; CNS-specific deletion of IL-33 leads to excess thalamic excitatory synapses and spontaneous epileptiform activity.\",\n      \"method\": \"CNS-specific IL-33 deletion, supraphysiological IL-33 dosing, ATAC-seq for enhancer landscape, MARCO-deficient mice, electrophysiology, synapse counting\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with defined synaptic phenotype, ATAC-seq mechanistic characterization, epistasis through MARCO\",\n      \"pmids\": [\"36520518\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Vitamin B6 (PLP) regulates IL-33 stability in epithelial cells via the MDM2 E3 ubiquitin ligase; MDM2 ubiquitinates the N-terminus of IL-33 to stabilize it, while PLP reduces MDM2-mediated IL-33 polyubiquitination and promotes IL-33 degradation through the proteasome pathway.\",\n      \"method\": \"Mouse models of lung inflammation, PDXK heterozygous mice, ubiquitination assays, proteasome inhibitor experiments, PLP inhalation therapeutic model\",\n      \"journal\": \"Cellular & molecular immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ubiquitination assay with identified E3 ligase, in vivo genetic model, functional rescue\",\n      \"pmids\": [\"37217797\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"IL-33 signaling through ST2 is required for IL-33-induced eosinophil homeostasis; IL-33 expands IL-5Rα-expressing eosinophil precursor cells in bone marrow, and IL-33-induced mature eosinophil expansion is dependent on downstream IL-5 production.\",\n      \"method\": \"IL-33-deficient and ST2-deficient mice, IL-5 neutralizing antibody, in vitro bone marrow stimulation, IL-5-transgenic mice crossed with ST2-deficient mice\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — dual genetic KO, antibody neutralization epistasis, in vitro mechanistic validation\",\n      \"pmids\": [\"27683753\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"IL11 stimulates IL-33 expression in human fibroblasts through STAT3 signaling; inhibition of STAT3 (but not MEK/ERK) prevents IL11-induced IL33 upregulation across kidney, lung, and skin fibroblasts.\",\n      \"method\": \"Primary human fibroblast cultures, RNA sequencing time course, STAT3 and MEK inhibitors, proteomic secretome analysis\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological pathway dissection across multiple fibroblast types with transcriptomic validation\",\n      \"pmids\": [\"36012165\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Staphylococcus aureus second immunoglobulin-binding protein (Sbi) directly drives rapid release of constitutive IL-33 from human keratinocytes via a Toll-like receptor-independent pathway; this IL-33 release is essential for the type 2 immune response to S. aureus in vivo.\",\n      \"method\": \"Fast protein liquid chromatography fractionation, mass spectrometry identification, recombinant Sbi expression, S. aureus Sbi mutant strains, ex vivo human skin explants, in vivo eczema-prone mouse model with IL-33 requirement validation\",\n      \"journal\": \"The Journal of allergy and clinical immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — protein identification by MS, recombinant confirmation, loss-of-function mutant bacteria, in vivo validation\",\n      \"pmids\": [\"33011245\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Sprouty2 loss in colonic epithelial cells activates PI3K/Akt signaling, leading to GSK3β inhibition and consequent epithelial IL-33 expression; epithelial IL-33 then promotes stromal IL-13+ cells and subsequent tuft and goblet cell expansion.\",\n      \"method\": \"VillinCre;Sprouty2F/F conditional knockout mice, PI3K/Akt pathway analysis, GSK3β phosphorylation, in vitro and in vivo IL-13 stimulation\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — conditional genetic deletion with defined signaling pathway and downstream cellular phenotype\",\n      \"pmids\": [\"33547321\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"IL-33 inactivates GSK-3β through an ST2-independent intracellular MyD88/TRAF6/RIP/PI3K/Akt pathway, and neutralizes amyloid β1-42-induced GSK-3β activation; siRNA knockdown of each pathway component confirms the signaling cascade.\",\n      \"method\": \"PC-12 cell siRNA knockdown of MyD88, TRAF6, RIP, PI3K; Western blotting for Akt and GSK-3β phosphorylation\",\n      \"journal\": \"Heliyon\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, single cell line, no in vivo validation, ST2 independence not fully characterized\",\n      \"pmids\": [\"30533546\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Fungal mycobiome-driven signals in PDAC cells increase IL-33 secretion, which recruits TH2 and ILC2 cells; cancer-cell-specific deletion of IL-33 reduces TH2/ILC2 recruitment and promotes tumor regression, placing IL-33 downstream of oncogenic KrasG12D and intratumoral fungal signaling.\",\n      \"method\": \"Cancer-cell-specific IL-33 deletion, KrasG12D mouse model, anti-fungal treatment, flow cytometry for immune cell infiltration\",\n      \"journal\": \"Cancer cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — conditional genetic deletion with defined immune cell recruitment phenotype\",\n      \"pmids\": [\"35120601\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"In asthma, genetic variants at the IL33 locus (tagged by rs992969) function as expression quantitative trait loci in bronchial brushes and cultured human bronchial epithelial cells; IL-33 overexpression in HBECs reduces viability and reactive oxygen species-capturing capacity.\",\n      \"method\": \"Lentiviral IL-33 overexpression in HBECs, eQTL analysis, regression modeling in cohorts\",\n      \"journal\": \"The Journal of allergy and clinical immunology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — limited mechanistic follow-up in overexpression cells, primarily eQTL analysis\",\n      \"pmids\": [\"32442646\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Asthma-associated SNP rs1888909 within a 5 kb enhancer-blocking element that loops to the IL33 promoter shows allele-specific regulatory activity through differential binding of OCT-1 (POU2F1), affecting IL33 gene expression in airway epithelial cells and IL-33 protein in plasma.\",\n      \"method\": \"Chromatin conformation capture (3C/4C), enhancer-blocking reporter assays in vivo and in vitro, allele-specific transcription factor binding (OCT-1)\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — chromatin conformation capture plus functional enhancer-blocking assay plus allele-specific TF binding\",\n      \"pmids\": [\"34675193\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Aspergillus fumigatus serine protease induces IL-33 expression in sinonasal epithelial cells via protease-activated receptor 2 (PAR2); serine protease inhibitor and reversible PAR2 inhibitor (GB83) block this IL-33 induction.\",\n      \"method\": \"Primary sinonasal epithelial cell cultures, irreversible serine protease inhibitor AEBSF, reversible PAR2 inhibitor GB83, qRT-PCR\",\n      \"journal\": \"The Laryngoscope\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological pathway dissection with two independent inhibitors targeting distinct steps\",\n      \"pmids\": [\"30973971\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Glutaredoxin-1 (Glrx) controls IL-33 induction in macrophages by regulating de-glutathionylation of TRAF6, which is required for TRAF6 activation and downstream IKKβ/NF-κB signaling; NF-κB is confirmed as a transcriptional regulator of IL-33 by ChIP-seq.\",\n      \"method\": \"Glrx knockout mice, siRNA knockdown in RAW264.7 cells, TRAF6 glutathionylation assay, NF-κB inhibitors, ChIP-seq\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO plus ChIP-seq plus NF-κB pathway validation\",\n      \"pmids\": [\"30682073\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"TNF-driven activation of TNFR2 in myofibroblasts stimulates IL-33 secretion; in turn, stromal cell IL-33 acts as a potent stimulus for TNF production from immune cells, forming a reciprocal signaling circuit between myofibroblasts and immune cells that drives fibrotic chronicity.\",\n      \"method\": \"Single-cell analysis of Dupuytren's disease tissue, in vitro stimulation assays identifying TNF→TNFR2→IL-33 and IL-33→TNF circuits\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — single-cell analysis plus in vitro pathway characterization\",\n      \"pmids\": [\"31840071\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"IL-33 signaling through ST2 in the developing brain promotes oligodendrocyte IL-33 expression via a positive feedback loop with microglia-derived IL-1β; IL-33/ST2 pathway orchestrates microglia and oligodendrocyte responses during Plasmodium berghei infection, with IL-33-driven microglia producing IL-1β which in turn stimulates further IL-33 expression by oligodendrocytes.\",\n      \"method\": \"ST2-deficient mice, PbA infection model, in vitro IL-33/ST2 pathway in microglia, IL-1β measurement, Ifng/Tnfa expression analysis\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ST2-/- genetic validation plus in vitro mechanistic loop characterization\",\n      \"pmids\": [\"28448579\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Polymerase 1 and transcript release factor (PTRF/Cavin-1) positively regulates IL-33 expression in bronchial epithelial cells; epithelial IL-33 then synergizes with house dust mite allergen to induce ZBP1 expression and downstream RIPK3/MLKL-mediated necroptosis in macrophages.\",\n      \"method\": \"PTRF knockout mice, Il33 deletion mice, HDM-induced asthma model, Western blot for RIPK3/MLKL phosphorylation\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — dual genetic deletion establishing pathway from PTRF to IL-33 to ZBP1/necroptosis\",\n      \"pmids\": [\"37454215\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"IL-33 induces eosinophilic esophagitis-like immunopathology in a transgenic mouse model through an ST2-dependent mechanism requiring IL-13; genetic deletion of IL-13 in IL-33-overexpressing mice abrogates all pathologic changes, placing IL-13 as the critical downstream effector of IL-33/ST2 signaling in esophageal inflammation.\",\n      \"method\": \"IL-33-overexpressing transgenic mice (EoE33), ST2-/- mice, IL-13-/- mice, esophageal organoids, steroid treatment\",\n      \"journal\": \"The Journal of allergy and clinical immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic epistasis experiments with clear pathway placement\",\n      \"pmids\": [\"38310974\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"TL1A cooperates synergistically with IL-33 to activate lung ILC2s, inducing a transient IL-9high GATA3low 'ILC9' phenotype; large-scale proteomics and intravital microscopy show that IL-9high ILC2s have increased capacity to drive IL-5-dependent allergic airway inflammation.\",\n      \"method\": \"Proteomic analyses, lung intravital microscopy, adoptive transfer of ILC9 cells, IL-33 + TL1A co-stimulation assays\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — synergy defined by co-stimulation, adoptive transfer of defined cell state, multiple orthogonal methods\",\n      \"pmids\": [\"38597952\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"IL-33 amplifies histamine-induced itch through a mast cell- and IL-13-dependent mechanism; mast cells are the dominant expressors of the IL-33 receptor ST2 in both human and mouse skin, and IL-33-stimulated mast cells significantly increase IL-13 production that mediates enhanced itch.\",\n      \"method\": \"Conditional and global knockout mice, IL-33 administration itch behavior assays, mast cell depletion, single-cell RNA sequencing of human and mouse skin, mast cell microarray after IL-33 stimulation\",\n      \"journal\": \"The Journal of allergy and clinical immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic validation in multiple KO lines, single-cell transcriptomics, mechanistic IL-13 link\",\n      \"pmids\": [\"37984799\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"IL-33 is a dual-function nuclear cytokine and alarmin that is constitutively expressed in epithelial, endothelial, and fibroblast nuclei via a chromatin-binding N-terminal domain; chromatin binding retards its release and it exits as a histone-IL-33 complex that synergistically activates the ST2/IL-1RAcP receptor complex to drive MyD88/IRAK/TRAF6/NF-κB and MAPK/ERK/JNK signaling, inducing type 2 immune responses through ILC2s, mast cells, Th2 cells, and eosinophils; additionally, IL-33 has ST2-independent cell-intrinsic nuclear functions (in Tregs and B cell progenitors), can be proteolytically activated by thrombin or other proteases, and undergoes oxidation to a non-ST2-binding form (IL-33ox) that instead signals via a RAGE/EGFR complex to drive epithelial remodeling, with its release regulated by P2Y13 receptor signaling, perforin-2-mediated export in DCs, PAR2 activation by fungal proteases, and MDM2-mediated ubiquitination controlling its stability.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2005,\n      \"finding\": \"IL-33 was identified as the functional ligand for the orphan IL-1 receptor ST2; binding activates NF-κB and MAP kinases and drives production of TH2-associated cytokines (IL-4, IL-5, IL-13) in vitro and in vivo.\",\n      \"method\": \"Receptor-ligand binding assays, NF-κB reporter assays, in vivo cytokine measurement in mice\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — foundational discovery with multiple orthogonal assays, highly replicated (3006 citations)\",\n      \"pmids\": [\"16286016\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"IL-33 is a chromatin-associated nuclear factor (identical to NF-HEV) with transcriptional repressor properties; nuclear localization and heterochromatin association are mediated by an evolutionarily conserved homeodomain-like helix-turn-helix (HTH) motif in the N-terminal domain.\",\n      \"method\": \"Immunostaining with multiple antisera, live-cell imaging, co-localization with mitotic chromatin, transcriptional repressor assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (immunostaining, live imaging, functional repressor assay), replicated extensively\",\n      \"pmids\": [\"17185418\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"IL-1 receptor accessory protein (IL-1RAcP) forms a co-receptor complex with ST2 to mediate IL-33 signal transduction; IL-1RAcP is required for IL-33-induced in vivo effects and dominant-negative IL-1RAcP blocks IL-33 signaling.\",\n      \"method\": \"Co-immunoprecipitation, dominant-negative constructs, in vivo functional assays\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP plus dominant-negative rescue, widely replicated\",\n      \"pmids\": [\"17675517\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Soluble ST2 (sST2) directly binds IL-33 in the fluid phase, preventing it from interacting with membrane-bound ST2L and thereby suppressing NF-κB activation and Th2 cytokine production.\",\n      \"method\": \"Direct binding assay (soluble ST2–IL-33 interaction), NF-κB reporter assay in ST2L-expressing EL-4 cells, murine asthma model\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct binding demonstrated, functional block confirmed in vitro and in vivo\",\n      \"pmids\": [\"17623648\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"IL-33 is constitutively and abundantly expressed in the nucleus of endothelial cells and epithelial cells in normal human tissues in vivo, establishing these cells as major sources and suggesting a dual role as an intracellular nuclear factor and extracellular alarmin.\",\n      \"method\": \"Human tissue microarrays, immunohistochemistry with monoclonal and polyclonal antibodies\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic tissue survey with multiple validated antibodies, widely cited and replicated\",\n      \"pmids\": [\"18836528\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Full-length IL-33(1-270) is biologically active and directly binds/activates ST2; caspase-1 cleaves IL-33 after Asp178 (not at Ser111 as previously proposed), resulting in IL-33 inactivation rather than activation. IL-33 is also a substrate for apoptotic caspase-3 at the same consensus motif (DGVD178G).\",\n      \"method\": \"In vitro caspase cleavage assays, ST2 binding assays, site determination by mass spectrometry, cellular activity assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with precise cleavage-site mapping and functional bioactivity assays\",\n      \"pmids\": [\"19439663\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Apoptotic caspases-3 and -7 (but not inflammatory caspases-1, -4, or -5) process IL-33, and this cleavage dramatically attenuates IL-33 bioactivity both in vitro and in vivo; caspase-dependent proteolysis acts as a switch to dampen IL-33's proinflammatory properties during apoptosis.\",\n      \"method\": \"In vitro caspase activity assays, ST2 binding assays, in vivo bioactivity models, caspase specificity panels\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with multiple caspases, confirmed in vivo, independently corroborates PMID 19439663\",\n      \"pmids\": [\"19559631\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Neutrophil serine proteases cathepsin G and elastase cleave full-length human IL-33(1-270) to generate mature bioactive forms IL-33(95-270), IL-33(99-270), and IL-33(109-270) with ~10-fold higher biological activity than full-length IL-33; these forms are produced by activated human neutrophils ex vivo and are active in vivo.\",\n      \"method\": \"In vitro protease cleavage, mass spectrometry cleavage-site mapping, neutrophil ex vivo assays, in vivo bronchoalveolar lavage model\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with precise site mapping confirmed ex vivo and in vivo\",\n      \"pmids\": [\"22307629\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"IL-33 amplifies IL-13-induced polarization of alveolar and bone marrow-derived macrophages toward the alternatively activated (AAM) phenotype via ST2L; IL-13/IL-4Rα signaling is required for this effect by upregulating ST2L expression. AAM-derived CCL24 mediates downstream eosinophil recruitment.\",\n      \"method\": \"In vitro macrophage polarization assays, alveolar macrophage depletion, ST2-knockout mice, cytokine neutralization\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic (ST2-KO) and antibody-mediated epistasis with in vitro mechanistic follow-up\",\n      \"pmids\": [\"19841166\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"IL-33 directly activates primary human mast cells to produce proinflammatory cytokines/chemokines via ST2L, and also accelerates in vitro maturation of CD34+ mast cell precursors.\",\n      \"method\": \"Primary human mast cell culture, cytokine ELISA, CD34+ precursor differentiation assay\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — primary cell assays with ST2L blockade controls, widely replicated (419 citations)\",\n      \"pmids\": [\"17675461\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Human eosinophils express ST2 (mRNA and protein), and IL-33 stimulates eosinophil superoxide anion production, degranulation, survival, and IL-8 production as potently as IL-5; anti-ST2 antibody blocks these effects.\",\n      \"method\": \"RT-PCR, flow cytometry, superoxide assay, degranulation assay, ELISA, antibody blockade\",\n      \"journal\": \"The Journal of allergy and clinical immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal functional assays with receptor blockade, widely replicated (414 citations)\",\n      \"pmids\": [\"18539196\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"IL-33/ST2 signaling is required for thermogenic licensing of brown and beige adipocytes during the perinatal period; in the absence of IL-33 or ST2, adipocytes fail to express correctly spliced Ucp1 mRNA and UCP1 protein, resulting in impaired uncoupled respiration and thermoregulation, despite normal adipocyte development.\",\n      \"method\": \"IL-33-KO and ST2-KO mice, RNA splicing analysis, UCP1 Western blot, metabolic/thermoregulation phenotyping\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with defined molecular phenotype (Ucp1 mis-splicing) and functional metabolic readout\",\n      \"pmids\": [\"27453471\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Nuclear IL-33 binds chromatin with ~10-fold lower intranuclear mobility than IL-1α (measured by FRAP); chromatin binding restrains necrosis-induced IL-33 release (slower, linear kinetics compared to truncated IL-33 or IL-1α) and IL-33 is released as a high-molecular-weight complex with histones that synergistically activates ST2-mediated signaling.\",\n      \"method\": \"FRAP live imaging, necrosis-induced release assays, size-exclusion fractionation, ST2-signaling reporter assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — FRAP quantification, biochemical fractionation, and functional synergy assay in one study\",\n      \"pmids\": [\"30108214\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"IL-33 induces cutaneous fibrosis in an IL-33R (ST2)-dependent manner, requiring IL-13 production and eosinophils; bone marrow-derived eosinophils secrete IL-13 in response to IL-33 stimulation, identifying eosinophil-derived IL-13 as a downstream mediator of IL-33-induced fibrosis.\",\n      \"method\": \"Subcutaneous IL-33 administration, IL-13 knockout mice, ΔdblGATA eosinophil-deficient mice, bone marrow-derived eosinophil stimulation assays\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — two independent genetic KO models with defined cellular and cytokine epistasis\",\n      \"pmids\": [\"20042577\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Nuclear FAK enhances IL-33 gene expression in squamous cell carcinoma cells; IL-33 associates with FAK in the nucleus and the FAK-IL-33 complex interacts with chromatin modifiers TAF9, WDR82, and BRD4 to promote NF-κB-driven CCL5 expression and immune evasion.\",\n      \"method\": \"Co-immunoprecipitation (nuclear FAK–IL-33 complex), ChIP, RNA-seq, shRNA knockdown, syngeneic tumor implantation\",\n      \"journal\": \"Science signaling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP and ChIP evidence for nuclear complex; single lab but multiple methods\",\n      \"pmids\": [\"29208683\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"FAK controls IL-33 gene expression by regulating chromatin accessibility at c-Jun/AP-1 motifs in the Il33 promoter/enhancer region; c-Jun binds the Il33 enhancer in a FAK kinase activity-dependent manner.\",\n      \"method\": \"ATAC-seq, RNA-seq, ChIP for c-Jun, FAK inhibition/overexpression\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ATAC-seq and ChIP provide mechanistic chromatin-level evidence; single lab\",\n      \"pmids\": [\"33420223\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"IL-33 promotes colon cancer cell stemness through ST2-dependent activation of JNK/c-Jun signaling, which drives binding of c-Jun to promoters of core stem cell genes NANOG, NOTCH3, and OCT3/4; IL-33 also recruits macrophages to produce prostaglandin E2, further supporting stemness.\",\n      \"method\": \"ChIP (c-Jun at stem cell gene promoters), phospho-JNK assays, ST2 pathway inhibition, in vivo tumor models\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP and phosphoprotein assays with pathway validation; single lab\",\n      \"pmids\": [\"28249897\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"IL-33 reduces macrophage foam cell formation via the ST2 receptor by decreasing modified LDL uptake (downregulating CD36), reducing cholesterol esterification (downregulating ACAT1), and enhancing cholesterol efflux (upregulating ApoE); ST2-deficient bone marrow-derived macrophages confirm ST2 is required.\",\n      \"method\": \"In vivo ApoE-/- atherosclerosis model, THP-1 and primary human macrophage foam cell assays, cholesterol efflux assays, gene expression, ST2-/- bone marrow-derived macrophages\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic (ST2-KO) and in vitro mechanistic data with defined molecular targets, in vivo confirmation\",\n      \"pmids\": [\"20543107\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"IL-33 activates SOCS3 expression to inhibit the IL-17 receptor signaling pathway, thereby reducing proinflammatory cytokine production in sepsis; IL-33 KO mice show increased mortality in cecal ligation-puncture sepsis, and this phenotype is linked to unrestrained IL-17 signaling from γδT cells.\",\n      \"method\": \"IL-33-/- mouse CLP model, in vivo cytokine measurement, in vitro MEF knockdown of SOCS3, IL-17 pathway phosphoprotein assays\",\n      \"journal\": \"Cellular physiology and biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with defined downstream pathway; single lab\",\n      \"pmids\": [\"28793286\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Cell-intrinsic IL-33 (ST2-independent) in regulatory T cells maintains their suppressive function; IL-33-deficient Tregs show NF-κB–T-bet-dependent epigenetic reprogramming (increased chromatin accessibility at the Ifng locus) leading to elevated IFN-γ production that impairs Treg suppressive capacity.\",\n      \"method\": \"Conditional IL-33 KO in Tregs, ATAC-seq, intracellular IFN-γ flow cytometry, in vivo tumor suppression assays, T-bet/NF-κB epistasis\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — epigenomic (ATAC-seq) plus genetic epistasis (T-bet, NF-κB, IFN-γ ablation) with in vivo functional validation\",\n      \"pmids\": [\"31844326\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"IL-33 expressed in dendritic cells (CD11c+ cells) promotes perforin-2 expression on DCs; perforin-2 acts as a plasma membrane conduit for IL-33 export from DCs, facilitating IL-33-driven expansion of ST2+Foxp3+GATA3+ Treg cells and mucosal immunoregulation.\",\n      \"method\": \"Conditional IL-33 KO in CD11c+ cells, conditional perforin-2 KO, flow cytometry of Treg subsets, ex vivo DC stimulation assays\",\n      \"journal\": \"Science immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — conditional KOs with defined cellular phenotype; perforin-2 conduit mechanism is novel single-lab finding\",\n      \"pmids\": [\"33188058\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Cell-intrinsic IL-33 (ST2-independent) in pro-B and large precursor B cells regulates early B cell development; IL-33 deficiency leads to increased E2F targets/cell cycle genes and decreased p53 pathway activity, resulting in increased frequency of developing B cells via a cell-intrinsic mechanism.\",\n      \"method\": \"Mixed bone marrow chimeric mice, RNA-seq of WT vs IL-33-/- pro-B cells, ST2 expression analysis by RT-PCR and flow cytometry\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — chimeric mouse epistasis plus transcriptomic mechanistic analysis; single lab\",\n      \"pmids\": [\"31391233\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"IL-33 activates mTORC1 in CD8+ T cells (evidenced by increased phospho-S6), and this mTORC1 activation drives upregulation of Glut1 and glycolytic enzymes, leading to increased glycolytic capacity (Warburg effect) and enhanced CD8+ T cell effector activation.\",\n      \"method\": \"Adoptive transfer experiments, phospho-S6 Western blot/flow cytometry, mTORC1 inhibitor rescue, glycolytic rate assay, Glut1 expression analysis\",\n      \"journal\": \"Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — phosphoprotein assays with pharmacological inhibitor rescue and metabolic functional readout; single lab\",\n      \"pmids\": [\"34411293\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Thrombin directly cleaves IL-33 at specific amino acids R48 and R106 to generate a mature bioactive form; low-molecular-weight heparin (thrombin inhibitor) restrains type 2 immune responses in mice by inhibiting IL-33 cleavage.\",\n      \"method\": \"In vitro protease cleavage with site-directed mutagenesis, in vivo papain/fungus/HDM/OVA airway inflammation models with thrombin inhibitors\",\n      \"journal\": \"Allergy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro cleavage with site identification confirmed in multiple in vivo models; single lab\",\n      \"pmids\": [\"34995358\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"IL-33 precedes IL-5 in regulating eosinophil commitment; IL-33 (via ST2) supports eosinophil maturation by driving systemic IL-5 production AND by expanding IL-5Rα-expressing precursor cells in bone marrow, establishing a two-step mechanism for eosinophilopoiesis.\",\n      \"method\": \"IL-33-KO and ST2-KO mice, IL-5 neutralization, in vitro bone marrow culture with IL-33/IL-5, IL-5 transgenic × ST2-KO crosses\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic models with cytokine-neutralization epistasis\",\n      \"pmids\": [\"27683753\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"GSK3β inhibition downstream of PI3K/Akt (induced by IL11 via STAT3) promotes epithelial IL-33 expression; IL11 is the most potent known inducer of IL33 in fibroblasts (38-fold upregulation), and STAT3 inhibition (but not MEK/ERK inhibition) prevents this induction.\",\n      \"method\": \"RNA-seq time course, STAT3 and MEK inhibitors, IL-33 protein quantification in primary human fibroblasts from kidney, lung, and skin\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological epistasis in multiple primary cell types; single lab\",\n      \"pmids\": [\"36012165\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Oxidized IL-33 (IL-33ox, non-ST2-binding form) forms a complex with RAGE and EGFR on airway epithelium, activating an ST2-independent pathway that impairs wound closure, increases mucus-producing cells, and induces epithelial remodeling mimicking COPD pathology.\",\n      \"method\": \"Co-immunoprecipitation of IL-33ox–RAGE–EGFR complex, in vitro epithelial damage assays, air-liquid interface models, single-cell RNA-seq, IL-33-neutralizing antibody reversal\",\n      \"journal\": \"The European respiratory journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — complex identified by Co-IP, functional consequences in ALI models plus scRNA-seq mechanistic characterization, therapeutic reversal\",\n      \"pmids\": [\"37442582\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PLP (active vitamin B6) regulates IL-33 protein stability by reducing MDM2-mediated polyubiquitination of the IL-33 N-terminus, leading to increased proteasomal degradation of IL-33 and attenuation of type 2 inflammation; PDXK heterozygous mice (reduced PL→PLP conversion) show elevated lung IL-33 and worsened type 2 inflammation.\",\n      \"method\": \"In vivo PDXK heterozygous and MDM2 knockdown mouse models, ubiquitination assays, proteasome inhibitor rescue, IL-33 stability measurements\",\n      \"journal\": \"Cellular & molecular immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ubiquitination assays with genetic mouse model confirmation; single lab\",\n      \"pmids\": [\"37217797\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"IL-33 inactivates GSK-3β through an ST2-independent MyD88/TRAF6/RIP/PI3K/Akt signaling pathway in PC-12 cells, and neutralizes Aβ1-42-induced Akt inactivation and GSK-3β activation.\",\n      \"method\": \"siRNA knockdown of MyD88, TRAF6, RIP, PI3K; Western blot for Akt and GSK-3β phosphorylation\",\n      \"journal\": \"Heliyon\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic siRNA epistasis; single lab, single cell line\",\n      \"pmids\": [\"30533546\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Asthma-associated SNP rs1888909 within a 5 kb enhancer-blocking element at the IL33 locus alters binding of the transcription factor OCT-1 (POU2F1) in an allele-specific manner, regulating IL33 gene expression in airway epithelial cells and IL-33 protein levels in plasma.\",\n      \"method\": \"Chromatin conformation capture (3C), in vivo and in vitro enhancer-blocking assays, allele-specific expression analysis (RNA-seq), OCT-1 binding EMSA\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — 3C looping, functional enhancer assays, and allele-specific OCT-1 binding with human tissue validation\",\n      \"pmids\": [\"34675193\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"A rare splice-acceptor variant in IL33 (rs146597587-C) causes intron retention with a premature stop codon, truncating the last 66 amino acids; the truncated IL-33 protein has normal intracellular localization but neither binds ST2 nor activates ST2-expressing cells, confirming the C-terminal IL-1-like domain is essential for receptor binding and activity.\",\n      \"method\": \"Whole-genome sequencing, allele-specific RNA-seq, recombinant truncated IL-33 binding and cell activation assays, cellular localization imaging\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — recombinant protein binding assay, population-scale allele-specific expression, and cellular localization in one study\",\n      \"pmids\": [\"28273074\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"IL-33 reduces CLDN1 (claudin-1) expression in keratinocytes through the ERK/STAT3 pathway; STAT3 directly binds the CLDN1 promoter to suppress transcription, leading to impaired skin barrier function.\",\n      \"method\": \"MAPK inhibitors, siRNA knockdown, EMSA/EMSA (STAT3 binding to CLDN1 promoter), TEER and FITC-dextran flux assays\",\n      \"journal\": \"Journal of dermatological science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — EMSA confirms direct STAT3–promoter binding; pathway confirmed by inhibitors and siRNA; single lab\",\n      \"pmids\": [\"29534857\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"P2Y13 receptor (a purinergic GPCR) acts as a gatekeeper of IL-33 release from airway epithelial cells; aeroallergen or virus exposure triggers extracellular ADP/ATP release that activates P2Y13-R, inducing nuclear-to-cytoplasmic translocation and subsequent secretion of IL-33; genetic deletion or pharmacological antagonism of P2Y13 ablates this response.\",\n      \"method\": \"P2Y13-R knockout mice, pharmacological antagonism, immunohistochemistry for nuclear-to-cytoplasmic translocation, ELISA, experimental asthma models\",\n      \"journal\": \"American journal of respiratory and critical care medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO plus pharmacological confirmation with mechanistic translocation readout; single lab\",\n      \"pmids\": [\"34860143\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Glutaredoxin-1 (Glrx) controls NF-κB-dependent IL-33 induction in macrophages by maintaining TRAF6 in its de-glutathionylated (active) state; Glrx knockdown impairs TRAF6 de-glutathionylation, blocks IKKβ/NF-κB activation, and reduces LPS-induced IL-33 mRNA; paracrine IL-33 in turn induces Glrx, creating a feed-forward loop.\",\n      \"method\": \"Glrx KO mice, siRNA knockdown, S-glutathionylation assay of TRAF6, NF-κB reporter, chromatin IP confirming NF-κB binding to Il33 locus\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP, post-translational modification assay, and genetic KO; single lab\",\n      \"pmids\": [\"30682073\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"IL-33 signaling in microglia promotes synaptic refinement by inducing an AP-1/FOS-driven gene expression program including the scavenger receptor MARCO; MARCO promotes synapse engulfment and CNS-specific IL-33 deletion causes excess excitatory synapses and seizure susceptibility.\",\n      \"method\": \"IL-33 supraphysiological CNS delivery, microglial enhancer landscape (ATAC-seq/ChIP), CNS-specific IL-33 KO mice, Marco-KO mice, synapse counting, EEG seizure monitoring\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — epigenomic profiling, two independent genetic KO models, and functional neurological readouts\",\n      \"pmids\": [\"36520518\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Staphylococcus aureus second immunoglobulin-binding protein (Sbi) is the predominant virulence factor that drives rapid release of constitutively stored IL-33 from human keratinocytes, independently of Toll-like receptor signaling and independently of necrosis; this IL-33 release is essential for the type 2 immune response to S. aureus in vivo.\",\n      \"method\": \"FPLC fractionation, mass spectrometry, S. aureus Sbi mutant strains, recombinant Sbi expression, in vivo NC/Tnd mouse model with IL-33 blockade\",\n      \"journal\": \"The Journal of allergy and clinical immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — protein identification by MS, confirmed with loss-of-function mutant bacteria and in vivo validation\",\n      \"pmids\": [\"33011245\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"IL-33 is a dual-function nuclear cytokine constitutively stored in the chromatin of endothelial and epithelial cells via an N-terminal homeodomain-like HTH motif; upon cellular damage or stress, full-length IL-33 is released (regulated by chromatin binding kinetics and conduits such as perforin-2) and signals through the ST2/IL-1RAcP co-receptor complex to activate NF-κB and MAPK pathways, driving TH2, ILC2, mast cell, and eosinophil responses, while its bioactivity is modulated post-translationally by neutrophil elastase/cathepsin G (generating hyperactive ~10-fold more potent mature forms), apoptotic caspases-3/7 (inactivating cleavage), thrombin (activating cleavage at R48/R106), MDM2-mediated ubiquitination (stability regulation), oxidation to a non-ST2-binding form (IL-33ox) that instead activates a RAGE/EGFR pathway, and nuclear sequestration by chromatin; intranuclear IL-33 also exerts ST2-independent cell-intrinsic functions in Treg stability, B cell development, and transcriptional regulation through interactions with FAK, chromatin modifiers (TAF9, WDR82, BRD4), and AP-1/c-Jun.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"IL-33 is a dual-function nuclear alarmin of the IL-1 cytokine family that couples tissue damage sensing to type 2 immunity, tissue repair, and developmental programs. Constitutively expressed in epithelial, endothelial, and fibroblast nuclei, IL-33 is retained on chromatin via its N-terminal domain and released upon cell damage as a histone–IL-33 complex that synergistically activates the ST2/IL-1RAcP receptor, engaging MyD88/TRAF6/NF-κB and MAPK/JNK cascades to drive ILC2, mast cell, eosinophil, and Th2 responses, with IL-13 serving as the principal downstream effector mediating fibrosis, mucus metaplasia, and eosinophilic inflammation [PMID:18613828, PMID:30108214, PMID:20042577, PMID:38310974]. Independent of its extracellular cytokine role, nuclear IL-33 functions cell-intrinsically in Treg cells—where it restricts Ifng locus accessibility to maintain suppressive identity—and in B cell progenitors, where it regulates E2F/cell cycle and p53 transcriptional programs, and it partners with nuclear FAK and chromatin modifiers (TAF9, WDR82, BRD4) to drive NF-κB-dependent chemokine expression in tumor cells [PMID:31844326, PMID:31391233, PMID:29208683]. IL-33 bioactivity is tuned at multiple levels: thrombin cleaves full-length IL-33 at R48/R106 to generate potent mature forms, P2Y13 receptor signaling controls its nuclear-to-cytoplasmic translocation and release, MDM2-mediated ubiquitination regulates its proteasomal stability, and cysteine oxidation converts it to IL-33ox, which cannot bind ST2 but instead signals through a RAGE/EGFR complex to drive pathological epithelial remodeling [PMID:34995358, PMID:34860143, PMID:37217797, PMID:37442582].\",\n  \"teleology\": [\n    {\n      \"year\": 2008,\n      \"claim\": \"Identifying that the orphan receptor ST2 (IL1RL1) together with the accessory chain IL-1RAcP forms the functional IL-33 receptor complex established the signaling entry point for this cytokine and placed it in the IL-1 family framework.\",\n      \"evidence\": \"Receptor binding studies synthesizing data from multiple labs\",\n      \"pmids\": [\"18613828\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of IL-33/ST2/IL-1RAcP ternary complex formation not resolved at this stage\", \"Downstream signaling cascades not yet mapped in detail\", \"Whether full-length vs. processed IL-33 differs in receptor engagement was unknown\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstrating that IL-33-induced fibrosis requires eosinophil-derived IL-13 established the key effector axis: IL-33 acts on eosinophils and ILC2s to produce IL-13, which mediates tissue remodeling.\",\n      \"evidence\": \"Dual genetic KO (IL-13−/−, ΔdblGATA eosinophil-deficient mice) with subcutaneous IL-33 administration\",\n      \"pmids\": [\"20042577\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether IL-13 is the sole downstream mediator or other cytokines contribute independently\", \"Mechanism by which IL-33 activates eosinophil IL-13 secretion at the signaling level\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Multiple studies revealed that IL-33/ST2 signaling controls diverse biological processes beyond classical type 2 immunity—including macrophage foam cell formation via CD36/ApoE regulation, eosinophil homeostasis via IL-5Rα+ progenitor expansion, brown adipocyte thermogenic competence via Ucp1 mRNA splicing, and microglia–oligodendrocyte crosstalk in the brain—establishing IL-33 as a pleiotropic tissue-context-dependent cytokine.\",\n      \"evidence\": \"ST2−/− and IL-33−/− mouse models with tissue-specific phenotyping (adipose, bone marrow, brain, macrophages)\",\n      \"pmids\": [\"27453471\", \"20543107\", \"27683753\", \"28448579\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of how ST2 signaling controls Ucp1 splicing is unknown\", \"Whether macrophage and eosinophil effects share common intracellular cascades or diverge\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Discovery that nuclear FAK directly binds IL-33 and recruits chromatin modifiers (TAF9, WDR82, BRD4) to drive NF-κB-dependent CCL5 transcription in tumor cells revealed a nuclear gene-regulatory function for IL-33 distinct from its extracellular cytokine role.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation, nuclear fractionation, syngeneic tumor models with genetic depletion\",\n      \"pmids\": [\"29208683\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the FAK–IL-33 complex has a broader target gene repertoire beyond CCL5\", \"Whether this nuclear function operates in non-transformed cells\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Functional characterization of a loss-of-function IL33 splice variant (rs146597587-C) showed that the C-terminal IL-1-like domain is essential for ST2 binding and signaling, while the N-terminal domain suffices for nuclear localization, genetically separating the two functional domains.\",\n      \"evidence\": \"Truncated IL-33 protein from human variant tested in ST2 binding and cell activation assays\",\n      \"pmids\": [\"28273074\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise structural determinants of ST2 contact within the C-terminal domain not mapped\", \"Whether heterozygous carriers show intermediate phenotypes in vivo\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"FRAP imaging revealed that the chromatin-binding N-terminal domain retards nuclear IL-33 mobility ~10-fold, and that IL-33 exits damaged cells as a histone–IL-33 complex with synergistic ST2-activating capacity, establishing chromatin tethering as a post-translational regulatory mechanism for alarmin bioactivity.\",\n      \"evidence\": \"FRAP in epithelial cells, biochemical fractionation of necrosis supernatants, receptor signaling assays\",\n      \"pmids\": [\"30108214\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of specific histone marks or partners within the complex\", \"Whether chromatin tethering quantitatively limits alarmin activity in vivo\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Cell-intrinsic, ST2-independent nuclear functions of IL-33 were demonstrated in two immune lineages: in Treg cells, IL-33 restricts chromatin accessibility at the Ifng locus via NF-κB/T-bet to maintain suppressive identity; in B cell progenitors, IL-33 regulates E2F/cell cycle and p53 transcriptional programs to control proliferative fitness.\",\n      \"evidence\": \"IL-33-deficient Treg-specific knockouts with ATAC-seq and IFN-γ rescue; mixed bone marrow chimeras with RNA-seq of IL-33-deficient pro-B cells\",\n      \"pmids\": [\"31844326\", \"31391233\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct chromatin-binding targets of nuclear IL-33 in Tregs and B progenitors are unidentified\", \"Whether nuclear IL-33 functions in additional immune cell types\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Multiple layers of IL-33 bioactivity regulation were uncovered: FAK kinase activity drives Il33 transcription through AP-1/c-Jun at the enhancer level; an asthma-associated SNP (rs1888909) within a 5 kb enhancer-blocking element modulates IL33 expression via allele-specific OCT-1 binding; and MDM2-mediated N-terminal ubiquitination stabilizes IL-33 protein, with vitamin B6 promoting its proteasomal degradation.\",\n      \"evidence\": \"ATAC-seq/ChIP with FAK kinase-dead mutants; chromatin conformation capture (3C/4C) with enhancer-blocking assays; ubiquitination assays with PDXK-heterozygous mice\",\n      \"pmids\": [\"33420223\", \"34675193\", \"37217797\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether MDM2 ubiquitination and chromatin tethering are coordinated regulatory events\", \"Full catalog of transcription factors controlling tissue-specific IL33 expression\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"IL-33 was found to orchestrate developmental synapse pruning by inducing MARCO on microglia, reshaping their enhancer landscape; CNS-specific IL-33 deletion caused excess excitatory synapses and epileptiform activity, establishing IL-33 as a neurodevelopmental organizer beyond immunity.\",\n      \"evidence\": \"CNS-specific IL-33 deletion, ATAC-seq, MARCO-deficient mice, electrophysiology, synapse counting\",\n      \"pmids\": [\"36520518\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether IL-33 acts through ST2 or a nuclear mechanism in this CNS context\", \"Source cell identity for IL-33 in the developing thalamus\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Three distinct mechanisms controlling IL-33 release and processing were delineated: P2Y13 receptor signaling triggers nuclear-to-cytoplasmic translocation and release from airway epithelium; perforin-2 serves as a plasma membrane conduit for IL-33 export from dendritic cells; and thrombin directly cleaves IL-33 at R48/R106 to generate potent bioactive forms.\",\n      \"evidence\": \"P2Y13-R genetic deletion and pharmacological antagonism; perforin-2-deficient DC experiments; in vitro cleavage assays with thrombin inhibitor validation in vivo\",\n      \"pmids\": [\"34860143\", \"33188058\", \"34995358\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether P2Y13 and perforin-2 pathways operate in the same or distinct cell types\", \"Complete protease repertoire that processes IL-33 in vivo\", \"Whether thrombin cleavage occurs in all tissue contexts or is restricted to coagulation-active sites\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Discovery that oxidized IL-33 (IL-33ox) cannot bind ST2 but instead signals through a RAGE/EGFR complex on airway epithelial cells to impair wound repair and induce mucus cell expansion established a second, ST2-independent extracellular signaling axis for IL-33 with direct relevance to COPD pathology.\",\n      \"evidence\": \"Air-liquid interface cultures, ST2-independence validation, single-cell RNA-seq, transcriptomic analysis of COPD airways\",\n      \"pmids\": [\"37442582\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for IL-33ox recognition by RAGE/EGFR\", \"Whether IL-33ox/RAGE signaling operates in tissues beyond the airway\", \"Kinetics of IL-33 oxidation in vivo\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Genetic epistasis in transgenic mice confirmed IL-13 as the critical and non-redundant downstream effector of IL-33/ST2 signaling in eosinophilic esophagitis, while TL1A was identified as a synergistic co-activator of IL-33-stimulated ILC2s that induces a transient IL-9high state driving allergic inflammation.\",\n      \"evidence\": \"IL-33-overexpressing × IL-13−/− and ST2−/− mice for EoE; proteomic/intravital microscopy and adoptive transfer for ILC9 phenotype\",\n      \"pmids\": [\"38310974\", \"38597952\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether TL1A/IL-33 synergy operates through shared or distinct transcription factor circuits\", \"Whether IL-9high ILC2 state exists in human disease\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the direct chromatin-binding targets of nuclear IL-33 in Tregs and other immune cells, the structural basis of the IL-33ox/RAGE/EGFR complex, the full scope of tissues where ST2-independent nuclear functions operate, and whether the multiple release mechanisms (P2Y13, perforin-2, necrosis) are differentially engaged across disease contexts.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No genome-wide map of nuclear IL-33 chromatin occupancy\", \"No structural model for IL-33ox/RAGE/EGFR interaction\", \"Relative contribution of each release pathway in specific diseases not quantified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [0, 3, 8, 11, 12, 22, 35]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [4, 7, 6]},\n      {\"term_id\": \"GO:0042393\", \"supporting_discovery_ids\": [1, 2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [1, 4, 6, 7]},\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [2, 18, 9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 3, 12, 22, 35, 36, 37]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 10, 13, 15, 26]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [4, 5, 29]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [7, 20]}\n    ],\n    \"complexes\": [\n      \"IL-33/ST2/IL-1RAcP receptor complex\",\n      \"FAK–IL-33 nuclear complex\",\n      \"histone–IL-33 complex\",\n      \"IL-33ox/RAGE/EGFR complex\"\n    ],\n    \"partners\": [\n      \"IL1RL1\",\n      \"IL1RAP\",\n      \"PTK2\",\n      \"MYD88\",\n      \"TRAF6\",\n      \"MDM2\",\n      \"AGER\",\n      \"EGFR\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"IL-33 is a dual-function alarmin cytokine that operates both as a chromatin-associated nuclear factor and as an extracellular ligand for the ST2/IL-1RAcP receptor complex, orchestrating type 2 immunity, tissue homeostasis, and damage responses across epithelial, endothelial, and immune compartments. Full-length IL-33 is constitutively stored in the nucleus of endothelial and epithelial cells, tethered to chromatin via an N-terminal homeodomain-like HTH motif; upon tissue damage it is released—often as a high-molecular-weight histone complex—and signals through ST2 to activate NF-κB and MAPK cascades that drive TH2, ILC2, mast cell, and eosinophil effector programs [PMID:16286016, PMID:17185418, PMID:18836528, PMID:30108214]. Bioactivity is tightly regulated by post-translational processing: neutrophil elastase and cathepsin G generate hyperactive mature forms (~10-fold more potent), thrombin cleaves at R48/R106 to produce additional active species, apoptotic caspases-3/7 inactivate IL-33, and oxidation converts it to a non-ST2-binding form (IL-33ox) that instead engages a RAGE/EGFR pathway driving epithelial remodeling [PMID:22307629, PMID:19559631, PMID:34995358, PMID:37442582]. Beyond its extracellular cytokine role, cell-intrinsic nuclear IL-33 maintains regulatory T cell suppressive identity by restraining NF-κB–T-bet–driven IFN-γ epigenetic reprogramming and regulates early B cell development through ST2-independent mechanisms [PMID:31844326, PMID:31391233].\",\n  \"teleology\": [\n    {\n      \"year\": 2005,\n      \"claim\": \"Identification of IL-33 as the functional ligand for the orphan receptor ST2 established that the IL-1 family includes a potent TH2-polarizing cytokine, resolving a long-standing gap in ST2 biology.\",\n      \"evidence\": \"Receptor-ligand binding assays, NF-κB reporter assays, and in vivo cytokine measurement in mice\",\n      \"pmids\": [\"16286016\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of IL-33 release from cells was unknown\", \"Whether IL-33 required processing for activity was unresolved\", \"Structural basis of IL-33–ST2 interaction not determined\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Discovery that IL-33 is a chromatin-associated nuclear factor (NF-HEV) with transcriptional repressor activity revealed its dual identity as both an intracellular regulator and an extracellular cytokine.\",\n      \"evidence\": \"Immunostaining, live-cell imaging of chromatin co-localization, and transcriptional repressor assays\",\n      \"pmids\": [\"17185418\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Nuclear targets of IL-33 repression were uncharacterized\", \"Whether chromatin binding regulates IL-33 release was unknown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Identification of IL-1RAcP as an obligate co-receptor for ST2 and of soluble ST2 as a decoy receptor defined the complete receptor architecture and a natural brake on IL-33 signaling.\",\n      \"evidence\": \"Co-immunoprecipitation, dominant-negative IL-1RAcP, direct sST2–IL-33 binding assays, and in vivo functional models\",\n      \"pmids\": [\"17675517\", \"17623648\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry of the ternary signaling complex was not resolved\", \"Mechanisms governing sST2 shedding were not defined\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Tissue-level surveys established endothelial and epithelial cells as constitutive nuclear reservoirs of IL-33, and functional studies showed IL-33 directly activates eosinophils and mast cells via ST2, defining the key cellular effectors of the pathway.\",\n      \"evidence\": \"Human tissue microarray immunohistochemistry; primary eosinophil functional assays with ST2 blockade; primary mast cell cytokine and maturation assays\",\n      \"pmids\": [\"18836528\", \"18539196\", \"17675461\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Release mechanism from intact cells was still undefined\", \"Relative contributions of mast cells vs. eosinophils in vivo unclear\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Reconstitution of caspase cleavage resolved the critical question of how apoptosis silences IL-33: caspases-3/7 inactivate full-length IL-33 rather than activating it, distinguishing IL-33 from IL-1β/IL-18 and establishing apoptosis as an anti-inflammatory checkpoint for this alarmin.\",\n      \"evidence\": \"In vitro caspase cleavage with mass spectrometry site mapping, ST2 binding assays, and in vivo bioactivity models\",\n      \"pmids\": [\"19439663\", \"19559631\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether other proteases generate active forms was unknown\", \"In vivo relevance of caspase-mediated inactivation during infection not tested\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Downstream effector biology was elaborated: IL-33 amplifies alternative macrophage activation via IL-13/ST2L crosstalk, drives eosinophil-dependent cutaneous fibrosis through IL-13, and directly induces mast cell cytokine production, establishing IL-33 as a master upstream regulator of type 2 tissue inflammation.\",\n      \"evidence\": \"Macrophage polarization with ST2-KO mice; ΔdblGATA eosinophil-deficient and IL-13-KO mice; bone marrow eosinophil stimulation assays\",\n      \"pmids\": [\"19841166\", \"20042577\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether IL-33 drives fibrosis independently of eosinophils in other tissues was unknown\", \"Direct transcriptional targets in macrophages were not mapped\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Discovery that neutrophil serine proteases cathepsin G and elastase generate hyperactive (~10-fold more potent) mature IL-33 forms answered how full-length IL-33 is activated in inflammatory microenvironments without inflammasome processing.\",\n      \"evidence\": \"In vitro protease cleavage with mass spectrometry site identification, neutrophil ex vivo processing, and in vivo bronchoalveolar lavage\",\n      \"pmids\": [\"22307629\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether mast cell proteases similarly process IL-33 was untested\", \"Relative contribution of each mature form in disease settings was unclear\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"IL-33/ST2 signaling was shown to license thermogenic gene expression (correct Ucp1 splicing) in perinatal adipocytes, extending IL-33 biology beyond immunity into metabolic physiology.\",\n      \"evidence\": \"IL-33-KO and ST2-KO mice with Ucp1 splicing analysis, UCP1 protein quantification, and thermoregulation phenotyping\",\n      \"pmids\": [\"27453471\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which IL-33 regulates Ucp1 splicing was not identified\", \"Source of IL-33 in the adipose niche was not defined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Nuclear IL-33 was found to form a complex with FAK and chromatin modifiers TAF9, WDR82, and BRD4, driving NF-κB-dependent CCL5 transcription in squamous cell carcinoma, revealing a direct transcriptional co-regulatory function and linking nuclear IL-33 to immune evasion.\",\n      \"evidence\": \"Nuclear Co-IP of FAK–IL-33 complex, ChIP at target promoters, RNA-seq, shRNA knockdown, syngeneic tumor models\",\n      \"pmids\": [\"29208683\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether the FAK–IL-33 nuclear complex exists outside squamous carcinoma contexts is untested\", \"Direct DNA-binding contribution of IL-33 versus scaffolding role not distinguished\", \"Awaits independent replication\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"A rare loss-of-function splice variant (rs146597587-C) truncating the C-terminal IL-1-like domain confirmed that this domain is absolutely required for ST2 binding, providing human genetic validation of the structure–function relationship.\",\n      \"evidence\": \"Whole-genome sequencing, allele-specific RNA-seq, recombinant truncated IL-33 binding and activation assays\",\n      \"pmids\": [\"28273074\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of C-terminal domain–ST2 interaction at atomic resolution not resolved\", \"Phenotypic consequence in carriers not fully characterized\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"FRAP and biochemical fractionation demonstrated that chromatin tethering slows IL-33 release kinetics during necrosis and that IL-33 exits as a histone-bound complex that synergistically enhances ST2 signaling, integrating the nuclear and alarmin functions into a unified release-and-signal mechanism.\",\n      \"evidence\": \"FRAP live imaging, necrosis-induced release kinetics, size-exclusion chromatography, ST2 reporter assays\",\n      \"pmids\": [\"30108214\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the histone partners in the complex not determined\", \"Whether histone association affects half-life in vivo was untested\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Discovery that oxidized IL-33 (IL-33ox) loses ST2-binding capacity but gains the ability to signal through a RAGE/EGFR complex revealed a second, ST2-independent signaling axis with distinct pathological consequences in airway epithelial remodeling.\",\n      \"evidence\": \"Co-IP of IL-33ox–RAGE–EGFR, air-liquid interface epithelial models, single-cell RNA-seq, antibody reversal\",\n      \"pmids\": [\"37442582\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of IL-33ox selectivity for RAGE/EGFR over ST2 unknown\", \"Relative abundance of IL-33ox vs. reduced IL-33 in disease tissues not quantified\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Conditional knockout studies revealed that cell-intrinsic nuclear IL-33 maintains Treg suppressive function by preventing NF-κB–T-bet-driven epigenetic reprogramming at the Ifng locus, establishing a major ST2-independent intracellular role in immune homeostasis.\",\n      \"evidence\": \"Conditional IL-33 KO in Tregs, ATAC-seq of chromatin accessibility, intracellular cytokine flow cytometry, in vivo tumor suppression, T-bet/NF-κB epistasis\",\n      \"pmids\": [\"31844326\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism by which nuclear IL-33 restrains T-bet/NF-κB access is not defined\", \"Whether this applies to human Tregs is untested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Cell-intrinsic IL-33 was shown to regulate early B cell development in a ST2-independent manner, with IL-33 deficiency increasing E2F/cell cycle programs and expanding developing B cell populations, broadening the nuclear functions beyond Treg biology.\",\n      \"evidence\": \"Mixed bone marrow chimeras, RNA-seq of WT vs. IL-33−/− pro-B cells, ST2 expression analysis\",\n      \"pmids\": [\"31391233\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct chromatin targets of IL-33 in B cell precursors not identified\", \"Protein-level mechanism (scaffolding vs. transcriptional) unclear\", \"Single-lab finding\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Perforin-2 was identified as a conduit for IL-33 export from dendritic cells, providing a non-necrotic secretory mechanism and linking IL-33 release to regulated mucosal Treg expansion.\",\n      \"evidence\": \"Conditional IL-33 and perforin-2 KO in CD11c+ cells, flow cytometry of Treg subsets, ex vivo DC stimulation\",\n      \"pmids\": [\"33188058\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether perforin-2 is the sole non-lytic export route is unknown\", \"Structural basis of IL-33–perforin-2 interaction not determined\", \"Single-lab finding\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Asthma-associated SNP rs1888909 was shown to alter OCT-1 binding at an IL33 enhancer element, providing a mechanistic basis for genetic regulation of IL-33 expression and disease risk.\",\n      \"evidence\": \"Chromatin conformation capture (3C), enhancer-blocking assays, allele-specific expression, OCT-1 EMSA\",\n      \"pmids\": [\"34675193\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full repertoire of transcription factors regulated by this enhancer not mapped\", \"Whether additional GWAS SNPs operate through the same element is unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Thrombin was identified as a novel activating protease for IL-33 (cleaving at R48 and R106), adding the coagulation cascade to the regulatory protease network and showing that anticoagulants can restrain type 2 immunity by blocking IL-33 maturation.\",\n      \"evidence\": \"In vitro cleavage with site-directed mutagenesis, multiple in vivo airway inflammation models with thrombin inhibitors\",\n      \"pmids\": [\"34995358\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relative potency of thrombin-generated forms vs. neutrophil protease-generated forms not compared\", \"In vivo evidence of thrombin-dependent IL-33 cleavage at steady state lacking\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"IL-33 in microglia was shown to drive an AP-1/FOS transcriptional program including MARCO upregulation that promotes synapse engulfment, connecting IL-33 to CNS synaptic refinement and seizure susceptibility.\",\n      \"evidence\": \"ATAC-seq/ChIP of microglial enhancers, CNS-specific IL-33 KO and Marco-KO mice, synapse quantification, EEG seizure monitoring\",\n      \"pmids\": [\"36520518\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether astrocyte- or neuron-derived IL-33 differentially contributes is untested\", \"Temporal window of IL-33-dependent synaptic pruning not defined\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"MDM2-mediated polyubiquitination of the IL-33 N-terminus was identified as a degradation pathway regulated by vitamin B6 (PLP), establishing a metabolic checkpoint for IL-33 protein stability and type 2 inflammation.\",\n      \"evidence\": \"Ubiquitination assays, proteasome inhibitor rescue, PDXK heterozygous mouse model with elevated lung IL-33\",\n      \"pmids\": [\"37217797\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific ubiquitinated lysine residues not mapped\", \"Whether MDM2 regulation is relevant in non-pulmonary tissues untested\", \"Single-lab finding\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the atomic-resolution structure of the IL-33–ST2–IL-1RAcP ternary complex, the precise molecular mechanism by which nuclear IL-33 restrains T-bet/NF-κB chromatin remodeling in Tregs, the full spectrum of non-lytic secretion pathways beyond perforin-2, and whether IL-33ox/RAGE/EGFR signaling is a general tissue damage pathway or restricted to airway epithelium.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic structure of signaling complex not solved\", \"Nuclear mechanism of Treg stabilization molecularly undefined\", \"Non-lytic secretion pathway incompletely characterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [0, 5, 7, 30]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [1, 14]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 26]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [1, 4, 12, 14]},\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [1, 12]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 5, 7, 12]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 8, 9, 10, 13, 19, 24]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 2, 3, 16, 26, 28]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [16, 26, 29]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [5, 6, 7, 23, 27]}\n    ],\n    \"complexes\": [\n      \"ST2/IL-1RAcP receptor complex (extracellular ligand)\",\n      \"FAK–IL-33–TAF9–WDR82–BRD4 nuclear complex\",\n      \"IL-33–histone release complex\",\n      \"IL-33ox–RAGE–EGFR complex\"\n    ],\n    \"partners\": [\n      \"IL1RL1\",\n      \"IL1RAP\",\n      \"PTK2\",\n      \"TAF9\",\n      \"WDR82\",\n      \"BRD4\",\n      \"AGER\",\n      \"EGFR\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}